People feel more qualified to pass judgement on things they think they understand than those which they do not. For some people being creative comes more naturally than mathematical equations, and vice versa.
The social sciences, professions (other than medicine) and philosophy also sometimes suffer from the same ignorant denigration, although they're seen as more respectable.
Also, anything barring some professions like medicine can be studied outside of university. You don't need a university to study theoretical physics or economics. In some cases it makes sense, but university being 'required' is just the outcome of the government trying to use universities as means of training people to be good wage-earners, rather the purely academic pursuits universities are intended for. I guess it works well for the professors who get paid bundles for teaching a few hours a week and then get to pursue their own research.
Most people think of degrees as investments (based on highly selective university statistics) but in fact they are ordinarily treated as consumption products, usually paid for by other people, too, and not just one's parents. That is fine but one should not be under the delusion that they are always an 'investment', or a good one, at that. Of course, I am not of the opinion that these degrees should be subsidised, so to me the whole thing is a matter of personal preferences and aptitudes. Also, I think if anything gets less 'respect' than degrees, it is the trades, which is a pity.