I have seen people in similar circumstances that have enormous personal blind spots for issues that show up in interviews and with past colleagues. It's much easier to blame AI rather than admit or address those. If you have 20 years of experience and no one wants to work with you again, that is telling.
I've worked primarily with offshore devs. I can't say that's been great for a network and if I'd known how bad of an impact it would have on my professional development due to effectively zero network, I'd have avoided it entirely. Healthcare IT is dominated by offshore so beware.
Many people only look at LinkedIn when they're on the job market themselves. Or do so infrequently enough that they only see the message weeks/months later, at which point it feels awkward to respond.
What if you're not the type to maintain relationships w/ former coworkers?
Anyone I once had the personal contact info of - which could now be stale - is also a contact on LI. It just seems like a less weird venue to hit up someone you haven't spoken to since you last worked some position. That's also been largely the case when old coworkers reach out to me.
The key thing is he did hit up what could be defined as his network and got nothing.
What surprised me is that the OP had no reaction for personal messages.