system
Given the following post, respond as if you're commenting on Reddit:
human
[My Hero Academia/Boku No Hero Academia] Why the hell don't heroes like cementoss use their quirks to do things like construction?

Cementoss has the power to mold concrete with his mind. We see him build that giant arena in the sports festival in what appear to be minutes. Wouldn't his talents be better spent doing things like creating low cost housing complexes in mere hours? Throw in some kind of metal bending/Magneto-like quirk user to work with him and they can cut that time down to minutes. It seems kind of a waste to have him be a hero.
gpt
Using your powers for productive purposes is by default illegal in the MHA Japan: You need a hero license to legally use your quirk in public, and that covers rebuilding after a disaster but probably wouldn't cover regular construction work. It's no surprise that lots of people ignore that law, but it's still on the books and sometimes gets enforced.

The logic behind it is presumably an attempt to prevent people like Cementoss putting construction workers out of a job.

Building the Arena was being done as part of a Hero contest for a Hero academy, so it's probably covered by the Hero License, but building a tower-block for regular people to live in probably wouldn't be.