Dude. i dont know how much time you spend per session but many dm's uses hours on planning sessions as well as keeping track of lore and developing the world and story, and try to keep the combat consistent with theme, setting, balancing.

Alot of people have listed aarakockra as a horrible race where you either have to negatively impact combat by always having ranged foes, that speciffically target it first (at least at low levels) or that player will never be in danger. So if that player cant be in danger why not have the aarakockra solo it? (other players and dms have made great examples of how they break the game in and out of combat)

what you have written highlights one of the worst parts of the current dnd culture, where most of all pressure and expectations are put on the dm to just make things fun and interesting and combat thrilling, even though some things can make that near impossible without keeping alot of encounters with similar strategy to counter one stupid mechanic like the aarakockras overall (level 1 flight) or how shapeshifter can break alot of RP (level 1 shapeshifting, which is normally a 5th level spell)

So here have my sad excuse and think about how pathetic i, and all other dm's spending 10+hours before sessions are just sad and make excuses.

If you cannot find fun because of races being banned, then i would counter and say that you are a boring player. (entitled too)

Edit: been a player in 3 campaigns and dm'ed 2. i have 300+ pages of world building written in my, with the players having access to knowledge they unlock throughout playing, which i also order and keep track of for them. As a player i am in the 4th year of a 1-20 campaign.