If at any point in time there is a way to tie your identity to _any_ of the transactions made in your lifetime, then all of your other transactions get deanonymized retroactively. Maybe you made a mistake, maybe a bug is introduced into the Bitcoin software, maybe the government passes a new law, etc.
Cash doesn't have this issue. The bills I'm paying with when buying coffee at Starbucks, don't give you visibility into all of the purchases I've made with cash for the past 20 years.
The only exception would be crypto like Monero, but it's not the rule. Bitcoin is the flagship coin which somehow got people to think it's anonymous.
All it takes is for the government to require you to use the same wallet that's tied to your identity and then every citizen's transaction, past or future, is traceable to a degree that is just not possible with cash. That's a dangerous capability and we, the people, should make sure not to slowly end up in such a situation.