USB flash drive is not just a form factor, it's a price point and a sellable market. The overall price of a USB flash drive is much less than than of a more costly SSD. This is because the drive manufactures need to cater to the already set target price point left over from the early 2000's. Simple economics is at play here. To get the lowest end user cost, the manufacturer must use the lowest sourced parts or take a large cut into profits. Manufacturers have to maintain a level of reliability with the public. If they completely cheap out, their public image falters and the public buys from another maker due to device failure and/or poor performance. SanDisk may claim to be using the same, but they are not. The parts may come from the same lines, but they're binned or altered to be a cheaper alternative. All part of the money game. Still stating they have the same internal controller and NAND is simply incorrect. One is designed to be used as an OS drive and the other is designed to carry files around in a mostly static state.
Your logic would follow the path that floppy disks would work as a start up drive for an OS (if theoretically there was a multi-gigabyte floppy). Just because it's slow, makes lots of noise, and is limited to only one read or write action at a time is irrelevant. Or maybe a better device, such as a circa 2002 1GB USB 1.1 flash drive. Completely unsuitable and would result in much end user aggravation, but completely able to run an OS on it. Even a 10 GB SCSI drive could be used as a start up disc. Slow, troublesome for the generic end user to correctly configure, and bulky. Completely unsuitable, but it could run an OS.
Now why are you still arguing the point. The question has been answered and we've gone far off topic.