it's not even the money to me, it's the contract terms these teams are giving away. I don't care if they pay a SS $50M/yr as long as he is on the field producing. It's the fact the even if they can afford it, teams remain very reluctant to just cut guys making >30M/yr even when they reach mere replacement level. So they clog up the lineup. That's the killer. Well maybe you hope he has a good year - after all he did two years ago for the half season before the nagging injury, or There's a lot PR value in his chase for 'X' (like maybe 3K hits?), or Man we are going to look dumb if we cut him and the knee/back/ankle improves and he puts up 5WAR for some other team on our money.
There is always a reason to hope against hope and give the guy one more year.
Iin the end, the opportunity cost is not in the dollars, it's in the roster spots.