I'm not suggesting this should be done because it always has been, just stating that it has been done, and that significant edition change can and has been a successful business tactic for WotC.
It was only really a successful business tactic from 4E to 5E.
Looking historically:
1E to 2E --> Not successful and drove TSR into bankrupcy
2E -->3E --> Successful only because 2E was dead. Kind of hard not to improve.
3.5E --> 4E Disaster
4E --> 5E This is the only complete edition switch that I would say was truely an unmitigated successful business decision.
Further when talking about backwards compatibility, we should also consider the 3E to 3.5E update which was a success.
Frankly I would argue the historical record, limited though it is, would indicate the opposite of your hypothesis: Going to a backwards-compatible updated version has always worked (the one other time it was tried), while bringing an entirely new edition to the table has generally not been a good business decision.
I also (and more importantly to my mind) think it is better creatively, as a proper 6e would allow the current designers of D&D, now soon to be under new leadership, to develop and more fully realize their design ideas under their current sensibilities and make a game targeted to the audience they want. And I believe games are stronger structurally, more interesting, and more fun when they have a clear design ethos and target audience.
I think it is likely a complete edition switch would have resulted in WOTC losing market share to 3rd party publishers in a fashion similar to how the 4E edition switch resulted in a massive market share loss to Paizo. The situation now is even more conducive to this than it was when 4E hit the streets.