Nobody would have offered Sony a big check for a lucrative license. This makes no sense.
There's other publishers who would have jumped at an official license. More competent developers than MLB's in-house efforts.
That's been available to them since the start of this gen and nobody bit. That's the reason MLB had to go in-house in the first place. The reality is that with cost of modern game development, the MLB license probably wasn't super attractive to other publishers, especially with Sony already owning so much of the pie.