"It's kinda sad that social media and advertising is the most lucrative businesses and so many bright minds work on that instead of for example ..."

So, how would you employ the engineers instead?

Industrial society is about producing garbage for the masses to consume. The huge churn of capital and labor creates as it's byproducts from time to time items of actual human value.

But those things would be fragile and complicated without the industrial economy surrounding them. If we look at this stage in our species history from far away, currently the industrial economy is supposed to be predictable and mundane.

So, "producing useless crap" is a required feature of our economy so it can occasionally produce science, art, medicine and the other things that actually improve us as a species.

Now, consumer goods fall into two categories: physical and digital. Physical consumer society is turning our biosphere to shit. Digital commodities, on the other hand, are much more lenient on the environment.

So, if we look at it this way, and presume that producing consumer crap is necessary for economic growth and stability, it's much better to work in producing digital goods and services rather than physical ones.

Within this framework, the actual question is not why do the brightest minds work at facebooks, but, will our economy ever develop beyond the point where producing useless crap is not so much a necessity for systemic stability rather than an occasional indulgence.