But it's what he's relying on to try to arrest the free-fall. He doesn't expect everyone to pay £100/year, but he expects a certain number to do so.

IMO, the cost of living crisis was one impediment, but the other, more significant one was the politicisation of it all. If he'd stayed neutral, and offered reliable, useful functionality behind that subscription, I would gladly have paid £5-10/month for the service. As it happens, I will almost certainly never subscribe to Twitter/𝕏 now.