Aside from the fact you generally need licenses to practice these professions, an additional challenge is you need lab equipment that may be expensive, regulate

Aside from the fact you generally need licenses to practice these professions, an additional challenge is you need lab equipment that may be expensive, regulated, or dangerous to acquire, to actually practice doing anything. I can't see any practical way to self-practice civil engineering in particular. Nobody is going to let you build a test bridge. Universities provide lab facilities for you to do this kind of thing. CS is the outlier because the only lab equipment you need is a used laptop or a Raspberry Pi and Internet access. Granted, computational engineering where you can just simulate the lab has come a long way, but even there, you generally need a lot of compute power if you don't want your simulation of a bridge to take 3 months to run.