Where Clubhouse is concerned, it's just... not social enough. If you load it when you don't know something special is happening, and just wander into random rooms, the chance of disappointment is high.
In that moment, it isn't competing with Twitter Spaces, it's competing with podcasts. I would bet most users of Clubhouse also listen to podcasts, and the chance that they can load up some audio that they know will be interesting is pretty high.
So Clubhouse's social network is weak. You can't just flip through Clubhouse real quick when you're stuck in line, and even when you have some time to kill, it's a crap shoot whether you'll find something fun. Where it really shines is special events, but that's not much of a moat.
Twitter and Spaces is synergetic, since Twitter is always there, ready to offer you an infinite scroll of witticism, cute cat pictures, and the Main Character of the Day. It's ok if Spaces is kind of useless unless there's a special event.
There's also the serendipity effect where you can be scrolling the timeline and see someone say "hey we're hanging out on Spaces", and just pop over.
Clubhouse has a head start, and some remaining halo effect, but no real moat, nothing to keep the conversation on Clubhouse. The big draws on Clubhouse all have Twitter accounts, they can try out Spaces any time they want. If it works for them, they switch, and if enough of them switch, it's over.
It's not inevitable, but it is something I'm starting to see happen in the circles I frequent.
He also hosts a space with other developers to discuss it each week. I usually listen in as well.