Yeah, life doesn't work like that. Of course it's a factor, but if anything, you could ask "why bother working my arse off when I'm already set for life?". He could literally stop being a footballer tomorrow and be better off than 99% of us on here.
It's like trying to understand why rich people have similar suicide rates to poor people - everything is relative to your situation.
Clearly he struggled with work ethic as a younger player, hence the stories of him being unfit. He found the motivation once to rise to the top, but staying there is a different challenge.
Either we find a way to unlock that motivation again, or move him on to somewhere and take a hit on the transfer fee. Its clearly a psychological issue.