But if you look at the market for business PCs back in 1981, it was completely open anarchy surrounding the CP/M-80 "8-bit PC standard". There were hundreds of vendors, including some big names in the computer industry. (IBM certainly didn't care about Commodore and etc. And as the article mentions, this took tons of support time from understaffed DR.)
So I think IBM quite strategically wanted to define the "16-bit PC standard", which they controlled for most of the decade. And Microsoft was the most compliant vendor. (There were antitrust restrictions on IBM too...)
On a larger level, it sounds like DR thought 16-bit was just a repeat of the early 8-bit computer industry and didn't really understand what IBM was up to.