We have 10 fosterers but rarely are all in use.. Mainly because that could be over 20 cats and we cannot afford to keep 20 cats in our care in one go and then continually. Also someof our foster have long term cats and some kittens etc.. So we could in theory have more then 20 or so with a few preg, kittens in our care.. Currently one cat can cost us 100 quid with vets etc... and we rarely get the donation to cover that..
We will soon be on our 200th rehomed cat and currently are vets bills (without the other expenses, food, litter) are near 1500 a month. So we cannot afford to get bigger, if you see what a mean..
Logistically more cats in pens means more money, volunteers etc, etc and we dont have the resources. So many branches do have a logistical limit
We could in theory take on another 2 fosterers (we have had people ask) but we decided 10 was enough for us all so we capped it for another year or so..