> what would be the benefit of running such closed apps in unmodified Linux VMs?
That you wouldn't need the official attested VM anymore.
> why would open-source Linux VMs trust closed apps with binary blobs?
The point is that with an open-source Linux VM, the user could decide what to trust instead of some megacorp deciding for everyone.
> vast corpus of mature open-source software applications
The problem is that there's a lot of proprietary apps that are both (1) necessary for a lot of real-world things, e.g., the SeatGeek app for tickets to shows, and (2) not replaceable with FOSS because the company will ban you if you connect to their API with a third-party client.
