I see you have been on Reddit for over 4 years, so you obviously have been around for a while, and should have a pretty good understanding of how subreddits work from user perspective. I don't see that you have been a mod of any subs, or any with over 160,545 users and 200,000 unique visitors. We are ranked 186 out of over 340,000 subreddits. Running a subreddit this big is like running a small city filled with people who don't like change, many being mis-informed, or reluctant to trying to learn and understand what is going on. On top of that, this is all volunteer and our only payment is the rage and hate in mod mail.

Part of our job is keeping 160,000 people happy, look out for what is best for the subreddit, which may not be what the users want, but what needs to happen to keep the subreddit moving in the proper direction. Any change is going to cause a stir, especially adding something that in the narrow field of view appears to be a huge inconvenience and has little to no positive gain. But, if you look at the big picture, can be REALLY beneficial. With smaller subreddits, they can make changes on a dime, and no one will really care. They are like a small family and they all understand. With something this big, we can't make a lot of changes quickly, or reverse directions on a dime just because initial feedback is bad. We fucked up with the sidebar. We hoped it would work, but it didn't and we could tell that it wasn't going to work and reversed the changes. That is an extreme case where we had to act fast and make change. The filtering of posts and other major changes are here to stay for a bit... until we can decide what to do.

 i honestly do not understand a) why it was implemented without actually asking the subreddit about it

With that statement you seem to be under the impression that every user has a say in what we do. The role of a moderator is to work in a similar fashion to the Congress/President of the Country/Senate/etc. They take advisement from a lot of sources, including the members that live in the country, they look out for the best interest of everyone, but they ultimately have the final say on what happens. No, this is NOT a dictatorship, but just like changes in a country, some things made will piss of those living there, and some changes we make will piss of users of this subreddit, but overall, we are looking out for the best interest of the majority. The users of this sub do NOT have the full picture. We see a LOT more than you do, and we don't have to ask for your permission on anything, and you don't run the sub, but we do seriously take your feedback/thoughts/opinions, and have made many changes people here have asked.

really and truly, why were they added?

They were added because users requested the ability to filter content. We are likely going to move away from required [bracketed] tags and make those optional and require users to click the flair button below their post to flair it instead. Having content flaired allows users to filter content. You may not want to filter content. 1,000 users may not, 1,900 users may not, but we have 200,000 users who visit here, read, and DON'T comment/post/upvote, but DO use this sub, and they may want to filter content. We have new users visiting this sub for the first time and allowing them to filter content can be very helpful for them, and for the livability of this sub beyond the next 2 weeks, but into the coming years.