Usually vets do not decrease their salary demands until they start to really, um, lose their talent skills in a big way. If they do, then the drop in contract demand makes perfect sense. Pro players will also demand less when their skills fade.
The 2nd concern: I have not seen this yet so I'd 1st ask if you have scouts and/or reduced ratings turned on. If so the AI may be seeing that the players true value is at the MLC level. The only time I recall seeing a MLC request is for young FA's or for some truly awful vets, and it's rare that any of them will have high enough ratings to play in the majors. It's possible I just have not seen good players request MLC's since most of my play involves strict house rules, but I am still skeptical about this. Maybe elaborate on what constitutes a major league level player in your opinion?