Knowledge it power, why are we stopping/hindering adults from continually growing?

Often it's intentional. The Republican party in the US is notorious for this, the insistence they keep their constituents ignorant (and let's be clear, there are far more people who are ignorant than stupid in this situation.)

Here in Canada there's a very strong 'anti-science' theme coming from the Right that has caught on. Often Conservative voters, when asked about policy, completely agree with, say the NDP or Liberal platform, but not when they hear the party name.

It's been shown time and again that people who vote conservatively are more easily swayed with fake news/obfuscation/Russian garbage, so as a society we have to be extra vigilant of it.