I can’t look up a conversation you had 5 years ago. I can look up a 5 year old tweet from someone who hasn’t logged in since. It wouldn’t be impossible to deal with that in a relatively rational way, but it would require twitter to spend time and money formulating a policy, and the gain would be very small.
Phone numbers on the other hand are a limited resource and before cell phones made it technologically desirable and feasible to port them between providers recycling them made a lot of sense. Though if we get low on them again I expect the solution will be to replace them with an alphanumeric identifier.