I think if you sent a message to https://squarp.net/contact they would have a more cogent answer for you but I have my suppositions… Here they are.
The delay doesn’t appear to have anything other than 1/ and I believe this is for a logical reason. I believe (though I am terrible at math) that 3/8 or 3/16 would divide down to one of the options that appear in the list. The divisions above 1/64 approach audio range and therefore tend to be less performatically useful.
Yes, it might just be another addition to a list, but it’s an addition that has to sit next to [on an encoder] and play nicely with music wise the other options around it.
I am literally schizophrenic so please take these suppositions with a grain of salt… They may be somewhat correct or entirely off base…