How many paid auth providers let you export user password hashes so that you can seamlessly migrate to another vendor, if you want to?
The whole problem with auth is that both (a) login screens are shown to unauthenticated users, which is a superset that includes attackers, who will do everything from DDoS to crafted malicious input to try to grab user secrets, so you really want to pick something that is already running at large production scale and with all the production battle-scars, and (b) that need to go with a managed vendor is very much in tension against local development, vendor independence, data portability, and other Good Engineering Practices (TM).
Sure, AWS Cognito sucks. In many ways, the product feels stuck. Making compromises to get stuff shipped, working, and stable sucks. But honestly, unless you're going to prefer (b) over (a) (and there are times to do so, in particular with intranet applications behind a firewall that aren't really susceptble to those kinds of attacks) and pick something like Keycloak, you could do a lot worse than Cognito (shudder, Okta, shudder).