> It still remains unclear to me how letting users opt out of making Twitter $0.55/month by giving Twitter, say, $4.95/month is a bad idea.

Hypothetically speaking, allowing those users to opt out would mean Twitter makes $0.20/month from the remaining users, rather than $0.55/month. Will enough users buy a premium subscription to make up that loss? I don't see the evidence that they would.

Of course, it's all hypothetical and none of us know the actual numbers involved. But I'd wager Twitter has looked at it at least once and decided it was not a good idea.