As with video live-streaming, highlighting relevant broadcasts can be challenging, because they’re evolving in real time, which can make it difficult to match for relevance.
If a broadcaster suddenly gets a few thousand people tuning into his or her chat, that will be a big motivator to keep broadcasting, and investing more time into Spaces as a medium.
Like, this is your platform, you can create simple tools that enable this type of filtering, without users having to know the expanded search operands to find things.
In fairness, Twitter is working on all of these things, and this is just a quick way to search for Spaces now.