Records follow incentives
A pipeline is maintained because a forecast depends on it. Nobody updates a closed-won opportunity, and nobody updates the people attached to it either.
The part that was never yours
There is a second reason, and it is structural. A shared pipeline belongs to the company. It is designed to survive you leaving, which is exactly what makes it a poor home for the relationships you personally built.
A record organised around people you know is worth very little to anyone else and a great deal to you. That is the whole argument for keeping it separate.