you are correct, there are tons of free IRs available but, typically that is what they're worth.
Making really good impulse responses requires exceptionally great gear and microphones, something most people don't have.
I do a lot of recording and it is nice to sample the room and get back to the studio with impulse responses of the same exact place where the concert or recording session took place.
I even made IRs of my old beloved Lexicon reverb so that if and when it goes poop, I will still have that awesome reverb at my disposal.
Altiverb is not for everyone, and if you do not do critical recording of string quartets, symphony orchestras, vocal groups, choirs and choruses, any decent reverb will sound good enough.