And, that's a shame, because the goals of "wander and explore the world" and "become super powerful" are inherently narratively interesting. Wanderers are frequently criticized as people who are more interested in the world than their neighbors, who can't be counted on. They're not heroes. Conan the Barbarian was this sort of person -- an interesting character, sure, but not your classic RPG hero, and definitely not treated like one.
The game will happily pause while you wander because they don't want to punish you for getting lost (you'd just restore from a saved game and take the quickest path anyway), and because - hey, the designers spent a lot of time and money developing these places. People consider it unfair to miss out on content because they were out exploring, and in that their goals coincide with those of the designers.
And really, the people who seek to become super powerful (ie: who sit and level grind) are worse. It's a fine thing to fight every monster you come across on the road from one town to the next. Gaining experience is only really incidental to the process of defending oneself. But it's entirely different for a powerful person or group of people to roam an area for the sole purpose of finding things weaker than they are to kill for their gold or simply for practice. In other forms of storytelling, these people are usually called "villains." But this is so routine for the PCs in most RPGs that it's not even commented on.
The notion of going out and finding things to kill so that you can practice your killing skills and as an afterthought strip their bodies of their gold (and occasionally a few belongings) to buy items that enable you to keep fighting is barbaric -- it ought to be abhorrent to the people in a game world, or at least some of the people. It's one thing to go out to the roadblock and kill the bandits there ("yay, you killed the bandits blocking the road! We can take our goods to market this afternoon!"), but another thing to immediately chase them back to their hideouts and slaughter them ("Holy crap, this guy is psycho!"). Most games would encourage (if not force) the latter option: the bandits won't leave (frequently this is assumed and not even stated), so you have to clear them out and fight the boss. But by the time you're stompy enough to clear out a group of bandits, they're probably not going to be willing to fight you. And the people who aren't horrified, the ones who are going to like your character and try to ingratiate themselves to him? You don't want to know those people.
The very goal of seeking power (ie: leveling up) is itself fundamentally incompatible with heroism: the best heroes in literature have always struggled with it. Power corrupts. It's useful and necessary, but it still corrupts. And even those who remain uncorrupted still lose something: Frodo understood that he could never really go home again, that his old friends would never look at him the same way. Why do RPG players rarely suffer that? They can almost *always* go home again (assuming it wasn't burned down as a plot point) and the people there will happily say the same dopey things and ask him to kill ten rats in exchange for a reward. There's never any downside to leveling up (except in the metagaming sense of having a less challenging game that's easier to breeze through to see more content), but there ought to be. Back in junior high, it was good to not be dumb, but woe betide the kid who was known as too smart. Too many of us thought it would be better to appear to be in the middle ground, to get things wrong on purpose to look a little more like everyone else. If the spunky little kid with spiky hair goes out, kills a whole lot of bad guys and comes back as a fucking juggernaut with giant mythical sword and glowing armor, surrounded by a half dozen lackeys who are armed to the teeth, people are going to smile and hand him the keys to the city and be very very polite. Maybe it'd be a good thing to lose a few battles, not look so invincible, make it look like it's still a struggle. It'd be even more poignant if the player were able to level up non-violently so as to look so invincible as to be able to win battles by intimidation without killing anyone -- the most virtuous could well suffer the most.
And maybe that's not really a choice: the ending of Fallout made it clear that there was no way for the Vault-Dweller to have his cake and eat it too. That's why I loved the ending to that game. If your plot requires the player to save the world, that character will have to be pretty damn stompy. But the great thing about most RPG players is that if you give them a hint that they *can* beat the bad guy but stay loved by all and sundry, that there is an "ideal" ending that they might be able to get, then they're actually crazy enough to try: they'll min-max and trade tips on forums and restore from saves and actually try to do it. In a metagaming sense, it seems somewhat tragic. (And of course, I'm the sort of jerk who would post and say that I'd done it, and post fake screenshots. I suspect that would get found out and result in backlash, but it would be awesome)
Part of the problem is that the level grind is an accepted substitute for difficulty control and careful game balance. (Besides, it's really hard to tell the difference between getting random encounters while fulfilling a task, getting them because you're basically just walking in circles hoping to get attacked, and getting them because you're lost and getting increasingly frustrated) Then there's the problem, how does a player defeat the bad guy if he chooses not to level grind? That might be a problem for the player to solve: how far does cleverness get you? But that has an impact on the plot: Does that mean that you can't escalate the plot to world-saving levels? If you gear the game design toward the middle of the road, then how do you intelligently deal with the folks who level up obsessively?