Why not?

You personally can refrain from any speculation, if you wish, but it's nonetheless the most obvious explanation. Moreover, your own speculation is implausible:

> perhaps this is a return to more profitable and credible roots.

This last-minute backpedaling makes The Washington Post look much worse than an endorsement. The new non-endorsement "policy" wasn't announced in advance. It came only after the editors had already drafted an endorsement of Harris, and at least one editor resigned as a result. The Post now appears less credible rather than more.