IBM doomed OS/2 with their earlier promise to MIS managers (as they were called then) that the PC-AT would be the last personal computer they'd have to buy for a long time.
Microsoft correctly hated the diversion of effort and compromises needed to get it to run on the 286 (which was truly awful when not being just a fast 8086) and didn't stop their Windows effort and at some point started up NT (well, we know the point, when DEC killed the Prism project, I just don't remember its relation to the other events).
This all came to a head when the 386 was the standard minimum CPU in a machine. OS/2 did not run competitively on it, Windows 3.0/1 could take significant advantage of it, was less complicated and imposing and I'm sure cost a lot less. And it could run multiple isolated DOS boxes.
That set the stage for what then happened.
There is a gray area between "clever" and "dishonest". Lotus trusted Microsoft, as did IBM. In retrospect, we know nobody should trust Microsoft.
Frankly, I am surprised that, at that time, IBM trusted Microsoft after the PC-DOS/MS-DOS PC-clone thing.
Not many people can fool me twice.
And, I have to say, Apple did fool me once: http://www.dieblinkenlights.com/blog_en/i-really-want-to-lik...