IMHO, ED's decision to maintain multiple version was likely based on the assumption that users would get too frustrated with the delay in both new content and progress in general. I doubt it was the most cost effective solution in terms of pure man hours, however, by doing it this way, they may well have been able to release paid content that otherwise would not have provided financial return until some time in the future.

The utility bills and the payroll are due now and IOU's don't cut it with some people.

Am I happy about it? Not really, but it is what it is and that is only a game that I try to enjoy.

A KSP update once ruined a year of exploration and left many kerbals stranded in outer space. That ticked me off more than many things about DCS's progress.