People on Reddit are simply too addicted to the content. That's the only real reason I can see what could bind someone to the platform. It all boils down to that - content. (And you probably don't need me to repeat the usual "for more content we need more users" lol)

The old reddit is purely a technical thing at this point. I believe in the popular opinion that it's a matter of time before it gets shut down.

I've personally been a user of it on Apollo and Relay and to me it was the way to use it. Rarely have I interacted with the website. So I imagine it's a similar thing with the old mode users.