So if a majority (say 75% or more) of users on a board voted and agreed on making a reasonable change (such as making a board sfw, nsfw, or creating new bannable offenses) why shouldn't they go into effect or at least some kind of trial mode?
Because 4chan isn't a democracy and never should become one. You're lucky to even be allowed to post here. You could be banned at any moment for an offence that you didn't commit, and I wouldn't have it any other way.
Because direct democracy would be a tyranny of the majority. The reason some of us use 4chan instead of some shitty social media site is because everybody here is on equal terms. It doesn't matter how unpopular your opinion is, you're still entitled to it. With your proposal in place, unpopular opinions (e.g. this could mean you) would become bannable offenses, and 4chan would be nothing more than an echo chamber where people regurgitate the same shitty opinions ad infinitum with no original thought ever permitted.
tl;dr - Fuck off
>thinks the majority of a board could ever be polled
Even if you were to discount lurkers, you'd have to be a fucking idiot for such a concept to pop into your head. Do you have any idea how many people use each board?