Looks like the UFS card interface only has one lane, but phones have been using two lanes for more performance for a long time. Samsung is planning a four-lane UFS solution for next year, but it's not clear whether that's intended for phones or laptops (their Snapdragon X Elite laptop uses UFS rather than NVMe). And the removable UFS cards standards have tended to lag behind by a few years on link speed, so it's really a 4x discrepancy in bandwidth between soldered UFS and removable UFS cards.
In theory, something like UFS cards could have performance parity with soldered UFS (at least for the link speed; not sure if a package that small is adequate from a power/thermal perspective when stuffed with 1TB of NAND). But UFS cards have been dead on arrival in the market several times now, so it's understandable that nobody wants to try an even more ambitious version in the hopes that it can finally catch on.
I think UFS might catch on if Samsung started cooperating with Samsung and Samsung to build a Samsung phone that would take Samsung UFS cards. Alas, I fear this can never happen, as Samsung wouldn't want Samsung's products to compete with their own storage tiers.
The problem with microSD vs UFS is that microSD is actually more than fast enough for most use cases if you buy good cards. Random I/O on SD cards is rarely a requirement even of phones with SD cards in them. Most of the time it's just bulk writing or reading video files and downloads.
Looks like the UFS card interface only has one lane, but phones have been using two lanes for more performance for a long time. Samsung is planning a four-lane UFS solution for next year, but it's not clear whether that's intended for phones or laptops (their Snapdragon X Elite laptop uses UFS rather than NVMe). And the removable UFS cards standards have tended to lag behind by a few years on link speed, so it's really a 4x discrepancy in bandwidth between soldered UFS and removable UFS cards.
In theory, something like UFS cards could have performance parity with soldered UFS (at least for the link speed; not sure if a package that small is adequate from a power/thermal perspective when stuffed with 1TB of NAND). But UFS cards have been dead on arrival in the market several times now, so it's understandable that nobody wants to try an even more ambitious version in the hopes that it can finally catch on.