What does soldering it to the board have to do with reliability?
If they were soldered onto those systems you talk about, all those would have had to be replaced instead of just having the drive swapped out and re-imaged.
I think the implication was that a soldered SSD doesn't give the customer as much chance to pick the wrong SSD. But it's still possible for the customer to have a different use case in mind than the OEM did when the OEM is picking what SSD to include.
It wouldn't solve other mismatched expectations. For example, the vendor might ship those SSDs only to store firmware-initiated crash dumps. They don't expect them to be used to meet production storage requirements. Maybe to occasionally boot a maintenance system, but that's it. To them, this is kind of obvious because everybody has a SAN anyway. But of course, this is not actually true in practice because customers vary a bit.
If they were soldered onto those systems you talk about, all those would have had to be replaced instead of just having the drive swapped out and re-imaged.