"Should domains be free after 30 years of registration if not transferred to a new owner?
Should accounts not be linked to email addresses or, even worse, phone numbers?"
That would be your opinion but not how things are. Domain registrations cost to maintain so what you do at the end is up to you.
As to the question about if you can remember all your accounts after 30 years, there are a few thoughts about that. Some keep that in their "little black book" and if you don't remember, maybe it's best forgotten.
Back to free. What you run the risk of here is sounding entitled. As these are businesses and not something like social security how would they pay for giving folk a free ride?
What do you do if you “Give up” your personal domain or say die. and not renew it, and someone else obtains it?
I have a personal domain and it hosts the email address I use to register most of my accounts online. So if I no longer have this domain, I would loose access to my accounts someone else could reset the passwords.
Most systems have a “forgot password” system that sends an email to the registered email address to allow reset. The new owner of the domain may well have set up the same email account and get the email, reset the password, and they are me, to the rest of the world.
Change all the email accounts you say, but can you remember all of the accounts you have after 30 years online? And if you are dead, you cannot. They would guess you have an account when the emails start to arrive, like Cnet ones.
OK Bank accounts should be shut down, but other things may not.
So I have to go on paying for my personal domain, for maybe another 30 years.
Should domains be free after 30 years of registration if not transferred to a new owner?
Should accounts not be linked to email addresses or, even worse, phone numbers?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic