It doesn't seem like sympathy is as wide spread as you think - the world is large and full of people, but only extremely small percentage of those people are actually capable of understanding and using sympathetic magic... and even for those that are, it doesn't seem like it necessarily takes much to mentally break someone and make them go insane. As a result, very few of those who are capable of learning it actually learn to use it and do so effectively, and even fewer of those people learn to use sympathy at an advanced level. Then there's naming, which much rarer than sympathetic magic.

For those that do go on to learn and perfect their sympathetic abilities, it sounds like most stay in the region near the university, and very few of those people stray away since their abilities wouldn't be understood, or even accepted in some of the more distant cities and regions (whether that's due to local law, superstition, or some other limitation to what and where they can use their sympathetic abilities). Also, just as others have mentioned, the university appears to have some way of keeping tabs on their students/graduates, and tracking them down in the event that those individuals are using violating any of the rules/laws of sympathetic use beyond the university (it kinda reminds me a little of Hogwarts).

There are some checks and balances to sympathy that are pretty cool, like how energy sources and other items are needed to perform certain tasks, and how those sources are usually consumed in some way. It creates some limitations to what can be performed, and now it's carried out, and many tasks require a pretty high skill level to pull off due to the dangers and risks involved.

I love it. There's such a strong natural element to it, and it isn't limitless (other than maybe naming, though naming still has some major limitations to those who haven't perfected their ability to connect with the names they know). I also really enjoy the fact that no one seems just automatically know how to do it all at an expert level. Kvothe is extremely talented and has a ton of natural ability, but he screws up often, which is a nice change of pace from the usual stereotype of those main/hero characters that just know how to do everything. It's unique in so many ways, and it adds even more depth to what already seems like a bottomless pit of lore in these books.