I think that the real motive for this change is getting lost in all of the uproar about the lack of notice.
Increasing the skill drop age to 35 makes every player more valuable. It is a little unintuitive, but I think this will actually cause transfer list prices to go down (or at least cause them to increase at a slower rate). My reasoning is that the supply of good, non-deteriorating players in the entire game will increase with this change, most prominently for D1-caliber players. Long-term, increased supply with constant demand should apply pressure on prices to decrease.
Anecdotally, it feels like the TL has had a lot of price inflation over the last 5+ seasons. Certain player archetypes are going for exorbitant amounts that are hard for most managers to afford. I actually think this change is an easy and elegant way to combat TL price inflation. Just because a change is simple and didn't require much engineering effort does not mean the ramifications weren't thought through and that it won't have a beneficial impact
[Side note: I'm curious if others agree with my perspective that TL price inflation has been rampant the last few seasons. I'd be VERY interested in getting my hands on a dataset that we could use to actually analyze this theory...]