You are missing the best solution which is your own domain and hosted email like Gmail. If you get locked out like you said, “just” change providers and you lose at most a couple of hours of emails.
Credit cards expire so manual action will be needed at some point, contact details change, people can be in financial troubles and even the ~€10 can be a lot, people can be temporarily indisposed due to illness (ranging from cancer to serious accidents to mental illness), etc. etc.
There's tons of exceptional circumstances where people can lose access to their domain. Some TLDs have no grace period at all and it can be fairly easy to lose access. For others it's larger, but even there, it's not that hard to see how people can lose access for one reason or the other.
There are registrars that let you pay ten years in advance. And of course, you should choose a reputable TLD. Seriously, this is not a problem in practice if you apply a minimum of diligence.
Some reputable ccTLDs don't have grace periods, and there may be good reasons for choosing such a TLD. Ten years is not the rest of your life (I hope, anyway) and you certainly won't be able to use the auto-renewal from your previous comment after 10 years. Sucks to be you if you happen to be in a hospital at that time I guess.
Are the chances small? Sure. But some are also outside your control and apply "small chance of [..]" to a large enough population and before you know it you're excluding millions of people.
To increase your chances with that issue, you pay for 10 years once, and then every year extend it by 1 year, giving you 9 years grace period in the worst case scenario (I don't know how but my providers allowed me to even stretch it to 11/10 years). If you're in a coma for 9 years that puts you on Wikpedia list of longest comas, so not really an issue. And if falsely imprisoned for that long, I think you can arrange something within that period to extend it.
No developer working on account authentication for sites has ever used the correct regex to parse and validate a legitimate email. I wouldn’t be surprised to see things like if you’re at anything other than @Gmail.com the email gets flagged as invalid. Maybe there’s a manual approval step here but better just flag your session as suspicious activity or failed bot check for the time being.
Or in the spaghetti parsing, obviously nobody is going to have swear words in their email. Go ahead and blanket ban all of that. And then @JohnsonAssociates.com gets banned.
I’ve also seen email parsing rules get applied to login screens too. So the valid email rules get updated and suddenly you fail validation trying to log into your already existing account. Ran into this today actually.
So having your own domain might solve some problems but you may still end up needing multiple accounts with devs refusing to use correct parsing rules.
Unless you're actively committing something that can be considered a crime in the jurisdiction of your registrar, you're unlikely to just loose it though. Unless you're hosting stuff at CloudFlare and they decide you're a "bad person", then anything goes.
Here's an additional problem with using your own domain: some websites (Discord for example) require you to contact support using the email tied to your account. Many corporate systems will reject emails from "untrusted" domains, so you won't be able to contact them.