[PassageNick]

(Note: I work for Passage.id, now part of 1Password...)

Auth is pretty easy to implement, but difficult to get and keep right. Then there are the nooks and crannies that crop up and appear and get discovered that you have to be aware of and keep up with. I am of course biased, but it seems to me that paying a company to keep up with the rapidly changing environment is much more efficient than trying to do it yourself.

And with WebAuthn and Passkeys -- you can implement that yourself without too much trouble. It's not trivial but not impossible, but the same argument applies -- nooks, crannies, corner cases, risks, etc.