Pro heroes in My Hero Academia take on a lot of different jobs, but the one that sticks out the most is teaching the next generation of heroes at UA and other hero schools. Most aren't actually suited to an academic environment, so why were these pro heroes selected as teachers rather than those who are? The truth has far more to do with what powers they have than their qualities as teachers.
While a number of pro heroes have been introduced in My Hero Academia, the pros who receive the most page time are those who train student heroes. Yet heroes like Eraserhead and Midnight aren't exactly suited to a school setting. While Eraserhead certainly cares for his students and has put his life on the line for them more than once, he's also prone to napping in the classroom and leaving them unmonitored, while Midnight has even been called out publicly for her inappropriate methods.Others, like class 1-B's teacher Vlad King, have personality flaws that are less than desirable in a teacher.
The answer lies in the nature of hero students themselves. In a world where using a quirk without a hero's license is illegal, each of these students is incredibly unfamiliar with their own quirks. Limitations, capabilities, and the potential for danger are all a mystery, so it's important to have more experienced pros around to help them learn and deal with exceptional situations. A student who begins to panic might cause untold damage with their quirk by accident, so it's important to have people on standby who can help to deal with that particular situation. Teachers like Eraserhead, whose quirk erases the quirk abilities of others, or Midnight, who can instantly put those around her to sleep, are incredibly useful should a student lose control, ending the danger in the blink of an eye. There are moments throughout the series where it's made clear that specific teacher quirks allow UA to operate as it does.
Many other members of UA's faculty have similarly handy abilities for the kinds of disasters students might bring about. Thirteen, Power Loader, and Hound Dog, for example, are rescue heroes; if a situation gets out of control, their quirks are ideal for locating students and removing them from danger. Recovery Girl's utility is obvious, as her presence ensures young heroes don't accidentally harm themselves and end a promising career early. Cementoss can repair the damage that students might do to school structures easily, while Present Mic's loud voice quirk can get messages out to any lost or trapped students. Much of the utility of UA faculty's quirks was seen early on, in scenarios like the USJ incident, even if that wasn't the exact scenario they'd been recruited for.
There are, of course, other benefits to pro hero teachers - such as teachers having connections with other active pros, helping to set students up with work-study and internship opportunities - but the choices seem to be based primarily on how practical their powers are when tutoring a bunch of untested superhumans. UA's principal Nezu is known for having a plan for everything, so it makes perfect sense that he'd recruit teachers who could best help keep students safe in an absolute disaster scenario. My Hero Academia's teachers may not be the best choices for teaching, but they are the best choices when it comes to keeping students safe, even from themselves.