In a lot of these acquisitions, it's not a becomes a subsidiary of b, it's often that all of the employees of A are transferred to B under something like a TUPE [0]. As part of these acquisitions, the leadership of the acquired team can be offered senior positions in the acquirer, e.g. in this case the CEO of AppLovin would become the COO of the new world.
Combine these two things and with a bit of luck and timing, AB corp now decided that A isn't in its best interests anymore and decides to sell that part of its business.
