Sales figures isn't what made this game. The development of this game is SO much more fascinating than many probably imagine, I'll love to talk about it in detail in the future but can't yet as it includes spoilers and some things better for someone else to reveal.
Essentially what happened is this game came into creation and was kept alive by pure passion of some of the devs. So this game was ORIGINALLY RE8, but in late 2017 it got turned into Rev 3 and stayed like that through most of development. A big reason the game did not go under was huge support by one of the series producers who kept pushing for this title to be made. Others in the company weren't as sure what fans of the franchise may think of it or that it might be "too weird" for Resident Evil.
But as Revelations 3 the game was 95% done late last year basically, it was fully playable and just being polished. They did some internal testing, and the reception to that was far, FAR more positive than they were expecting. People who didn't work on the game but work at Div 1 also played it and were surprised how good it came out.
The Ambassador Test held last year was to test it with more direct fans as they were toying with the idea of it being RE8, but they weren't sure what fans would think. However, the test, plus some other stuff (and especially the fact the other RE8 was years away from completion), meant Revelations 3 got an upgrade.
But the existence of the game has nothing to do with anything, it was a pure passion project by some people on the studio, which managed to be made and was originally kinda' thrown into a Revelations game as it's a side series, but due to circumstance and the actual quality of what was made, it gets a bigger chance to shine and gets an additional year to build onto it, polish it, etc.