Well, 3.5" SSDs are certainly possible, but 2.5" (or in fact m.2) might just be a better form factor for SSDs. The thing is, an SSD is just a bunch of chips on a PCB, so they really don’t need the extra height afforded to them by a 3.5" bay.
You could probably fit 2 pcbs one on top of the other within a 3.5" drive, but that would probably need a third PCB to connect the two which would be more complicated to manufacture and be worse for cooling than using two individual 3.5" or m.2 cards.
Also, for a bunch of reasons smaller is usually better. Generally, it tends to be cheaper to use a few large capacity chips on a small board than it is to use a lot of lower capacity chips on a larger board. Of course fewer parts also means fewer potential points of failure, so better for quality control. And again, smaller cards are better for case airflow and cooling.
Well, 3.5" SSDs are certainly possible, but 2.5" (or in fact m.2) might just be a better form factor for SSDs. The thing is, an SSD is just a bunch of chips on a PCB, so they really don’t need the extra height afforded to them by a 3.5" bay.
You could probably fit 2 pcbs one on top of the other within a 3.5" drive, but that would probably need a third PCB to connect the two which would be more complicated to manufacture and be worse for cooling than using two individual 3.5" or m.2 cards.
Also, for a bunch of reasons smaller is usually better. Generally, it tends to be cheaper to use a few large capacity chips on a small board than it is to use a lot of lower capacity chips on a larger board. Of course fewer parts also means fewer potential points of failure, so better for quality control. And again, smaller cards are better for case airflow and cooling.