It wasn't - it's become a rallying cry and it was totally organic. Never seen anything like it.
I think the "we're not going back" thing is a good pushback to the GOP. It's a chance to flip the narrative from the GOP being able to say "we can make it better" to the Democrats being able to say "no, they will make it worse - and they wrote a book on how they will do it (Project 2025)." The GOP wrote down exactly how they plan to govern and a lot of it is very unpopular.
That said, wet blanket time for the Democrats:
The Democrats have a lot of momentum right now, but inflation and a tighter job market still loom large over everyone's lives.
Yes, gouging is a thing and so is corporate greed, but all the average person knows is things are more expensive and it's harder to find a job. Inflation has slowed, but things are still more expensive and wages haven't kept up. Those are facts and voters need someone to blame. The Democrats were in the White House as that occurred and there isn't an easy counter like there is on immigration with Trump killing the border bill.
The good news for the Democrats is that Trump and many of the GOP candidates are terrible and can't stay on message to save their lives - and it's easy to pull them offsides with psyops like filling their convention arena on the night of the "official" nomination.