Its annoying and ive seen like 5 interesting questions asked and all answers have been deleted.
This is a strictly moderated subreddit, and we remove comments that don't fit our high standards. (To be precise in the language, all we subreddit moderators can do is remove comments; only the original poster of a comment can delete it, but I get what you're asking.)
That said, we don't remove every comment on posts here; we figure we remove about a third of all comments (and that number is largely influenced by posts that hit r/all and get dozens or even hundreds of comments that don't meet those standards, and then get removed.
Overall, about 40 percent of all questions asked here get some kind of answer, either an original answer or a link to an older answer. For the infamous "comment graveyard" threads that hit r/all, we actually have a much higher response rate, well over 90 percent, though it can take time for an answer to appear. u/Georgy_K_Zhukov crunched numbers on this awhile back: https://www.reddit.com/r/AskHistorians/comments/7s66yf/a_statistical_look_at_askhistorians_in_2017_part_i/
So my guess is that if you're seeing threads with removed answers, you're seeing them early in their "life cycle" before answers that meet our standards appear. If you just want to read cool questions and answers, you can also check out our Twitter, the Sunday Digest, the Monthly "Best Of" feature, and Facebook.
Edit: I a word
I'm sure someone will be along shortly to talk more about this, but you might be interested in previous threads on this topic: