It also has a lot of parts that can be harvested to keep its Six Flags-owned siblings alive longer (its Texas clone and the three remaining spaghetti bowl models). Over Texas is getting a major coaster next year already and, frankly, being a Texas Six Flags, Mr. Freeze South may have some special plot armor that St. Louis' doesn't enjoy. Speaking of special Texas Six Flags plot armor, Poltergeist recently got a huge thematic update so there's definitely an extra reason for the chain to try to keep it running longer. Meanwhile, the two Flight of Fears are indoors and likely benefit condition-wise from that fact compared to the others.
It's easy for me to imagine St. Louis' Mr. Freeze being the next early Premier to follow in Joker's Jinx's footsteps, unfortunately. That said, as much as I'd hate to see Mr. Freeze North die, if SFStL can get a good, substantial, much more reliable, modern launch coaster out of the deal, that's a trade they should definitely take if you ask me. Sorta a no-brainer.