It could actually just be a way of forcing them to obey the law, by negotiating all the way to the closure date, and then still blocking it, because Microsoft won't back down.
Being unable to get a schedule that would allow them to get suitable representation will also have been a factor, because it is a consenting delay from Microsoft, as the pause in legal action will cause that time table to move backwards to the CMA's advantage.
It might also be that their behind the scenes discussions with OFCOM means fighting this might be worthless if OFCOM are intending to legislate heavily for Cloud and Cloud gaming competition, so service costs might be a level playing field for all - including Microsoft as the old BT- just like access to the national telecoms network (OpenReach formerly BT) is the same to all least-cost-routing providers, today.
The pause in legislating might also mean the 10% fine issue would now be active, and no longer a new law, not applying to an old offense.