1. USB flash drive? are you sure it can get at least 5 GB/s for read/write speed? for the next generation of console (in around 2026; PS6 or whatever Xbox's next console is), most probably it needs higher speed; maybe 10, 15 or even 20 GB/s.
2. USB flash drive has too small form factor for physical game storage, making it easier to lose. that's why I prefer NVMe PCIe SSD because the physical size is still large enough.

but the speed. an optical disc doesn't have the same read-write speed as that of an NVMe PCIe SSD. what we (or at least I) want is a non-volatile storage with high speed, used for physical games.

of course someone is gonna pop up the issue of the SSD production cost. it was similar to the case of cartridges back then (more expensive than CD-ROM at the time), but the difference is that SSD, of course, has more capacity (up to 4 TB, although only the 256 GB and 512 GB variants will most likely be used for modern physical games) than that of the latest optical disc technology (4K UHD Bluray, with "only" up to 100 GB), while cartridges back then had less capacity ("only" up to 64 MB) than that of CD-ROM (which is up to 600 MB).