As C-Dub mentioned, ABK wants to sell, and among the very short list of entities with the wherewithal to buy it, Microsoft is pretty much the least bad of all the choices. Tencent? The Saudis?
Consider the following effects of Microsoft picking up ABK:
1) It helps keep MS competitive vs. Sony. Not hamstringing SIE's ability to compete, because even post merger they will remain a pretty clear no. 1. But there would at least be enough wiggle room for Xbox to remain relevant, and retain a respectable amount of market share, thus keeping PlayStation on its toes.
As it is, SIE is getting away with leveraging its market position to secure timed exclusives (which also affects PC customers like us) at minimal cost, because in the event of a day and date launch the majority of customers would be buying the PS5 version anyway. So they have to pay less to get these deals signed.
2. It guarantees a baseline level of profitability for the Xbox division for the foreseeable future. Each division of MS essentially operates independent businesses; if a certain business really shits the bed, it's possible that MS seniors decide to change course entirely. Having ABK around ensures that the Xbox gaming unit gets recurring annual income from CoD (in a non-exclusive capacity, so including Playstation SKU sales), WoW and Candy Crush.
Just to be clear, I'm primarily a Steam/PC customer, and on the console side I historically buy PlayStation and Nintendo consoles (the XSX is my first Xbox). This isnt plastic box BS, but mere pragmatism.
I understand your concern - I lived through Embrace Extend Extinguish, and Games for Windows Live, so I'm well aware of Microsoft's less than sterling reputation. But I am certain that the worst thing that could possibly happen, for all of us, is Sony running entirely uncontested. A competitive Xbox, even just as a foil for Sony, benefits us all.