EDIT: Another great example is the stunt Intel pulled with AVX to intentionally sabotage AMD's ability to compete in the market, as documented here:
Essentially, Intel published a proposed new instruction format, and AMD said 'that looks great, we'll be compatible with it'. After AMD announced this and had started preparing to ship their new chips, Intel suddenly announced that they had changed their instruction format from what they published - after it was too late for AMD to adapt.
The end result was AMD shipping chips that were incompatible with Intel's despite AMD's best effort. Intel knew that as the majority market share holder, developers would prioritize Intel compatibility over AMD compatibility, and AMD would lose.