I'd understand if the only offers were from relegation candidates and such, but if he's had offers from the likes of Tottenham, a fairly big club where cup trophies and CL qualification are very much within the realm of possibility, it says a lot about him. Maybe there's a correlation between his atrocious performances and his apparent preference for collecting his pay from a permanent place on the bench. If he actually wanted to play as much as possible and revive his career, a move to a club like Tottenham, or even Villa who seem to be on the rise, would make all kinds of sense.
Choosing to piss the rest of his career away on the bench, just to squeeze more money out of it for now, falls right in line with what he shows us on the rare occasion that he does play. And in the long term, will that even result in more money earned once he does retire? It's not as if we'll renew, and who would take him if he has sat on the bench for three more years? That's when the only offers will be from clubs at the bottom of the league, or even the Championship. There's every chance that he could move on now, with a moderate drop in pay, but actually play regularly and end up making more money in total by the time he retires, than if he sits on the bench until 2026 and then goes to Wigan or whoever will have a man who has languished for several years.
One thing that has to happen, and which may also help nudge him out of the door, is for ETH to revoke his captaincy and give it to someone more deserving. We can't have a captain who barely plays, and he doesn't deserve to play more than he has lately. Even when he does play, there are no apparent signs of leadership from him. We can safely assume that none of the other players think highly of his footballing credentials, given that he is de-facto one of the worst players at the club these days, so the only way in which it would make sense for him to remain captain (if we pretend that he actually did play with any kind of regularity) would be if he had a strong aura of leadership. There's no indication whatsoever that he does.