There’s multiple reasons. For one thing, we are the exception. Most teams already have a very quality backup and there’s only 32 of those jobs available. Secondly, he’s seen as someone you tailor an offense to, not someone who can just jump into any system - not something most teams are looking for in a backup.
If we tinker the offense to center around his strengths, he’s at least shown a glimmer of potential which could give us a tiny bit of hope. No one should hold their breath, but I can at least feel like we have a punchers chance with him out there. Not so much with Boyle and Thompson.