[Publius]

Because they need to do it at the convention, rather than now. If they do it now, everybody and his sister will re-declare candidacy, and it will be chaotic. Money will flow in all directions, and most of it will be wasted.

At the convention, Biden steps aside, and the DNC brass inserts a different candidate. There will be a show of unity, and money will flow in the right direction. The Sandernistas will be he only people to complain.

[blu]

But...aren’t there time limits as to when a candidate has to declare so they can be on the ballot?

[Bigg Red]

Your analysis makes sense.