The objective behind verifying accounts is to prevent spammers creating lots of spam accounts and using those to spam.
However, spammers rarely care if their spam is encrypted, so putting E2E behind verification won't do anything as far as spammers are concerned - they'll happily keep spamming using the unencrypted accounts.
There's some other reason behind this that isn't about reducing spam.
The objective behind verifying accounts is to prevent spammers creating lots of spam accounts and using those to spam.
However, spammers rarely care if their spam is encrypted, so putting E2E behind verification won't do anything as far as spammers are concerned - they'll happily keep spamming using the unencrypted accounts.
There's some other reason behind this that isn't about reducing spam.