I run an MTA sending billions of emails daily. Most mail is delivered in seconds, but there is a long tail that can take days (myriad of reasons involving recipient mail servers, dns, sending behavior , etc). It would not be fun to have your log in attempt come in a couple days later. 99.9%+ you will be just fine, but how do you handle those people who fall through into long-delay land?

email is supposed to be dependable - as a protocol - it should always arrive. This dependability comes at the price that in some edge cases it must arrive slowly. There should be no 'never' arrive, although I realize that many services now effectively keep email from actually being seen by the user in the name of combating the various problems a free, anonymous, dependable message delivery protocol inevitably give rise to.

I have both a personal G Suite domain (formerly "Google Apps For Your Domain") and my employer's G Suite account where in both cases I've experienced 5+ minute delays on a semi-frequent basis.

Thirty seconds is not instantaneous and is much slower than typing a password. The only server that shows mail the instant it's sent is the one I run for my personal use, which is a bad solution for most.

"never" doesn't feel instantaneous though.

Joking aside, email never coming is a pretty common occurence for me on new services, especially small orgs (local clubs, small merchants)

That's great, good for you! But E-mail is not guaranteed (nor designed) to be instantaneous.