>I suspect the reason IBM was able to reconcile with Linux and even go all-in on it was that it complemented their lucrative very high end server and mainframe businesses.

Linux also gave IBM for the first time an OS that ran on all its hardware, from low-end x86 to POWER workstations to xSeries/iSeries minis to mainframes to supercomputer clusters, a goal it achieved with System/360 in the 1960s then soon had to abandon when the minicomputer and PC markets emerged.