I always took the jar of Snokes/Palp clones as ‘used’ or failed experiments, not new growing organisms. The Jar of Snokes seemed like leftovers from the experiments that resulted in THE Snoke, and likewise the old Palpatine bodies seem like either failed attempts or bodies that were used and ‘exhausted’ by Palpatine’s spirit.
I interpreted it this way too. I like this explanation. It’s why Palpatine is so desperate for at least the energy of a new host all together; the cloning stuff ain’t working.