@Zoo adventures It's a long explanation (and as the designated TZ hyena guy I'm the one who gives it lol) but we unfortunately don't breed our hyenas for multiple reasons.
First off the main reason is something you mentioned yourself. We have four, and four is too many for us to add cubs. The hyena barn is very small (how that thing held a pride of lions back in the olden times is beyond me but zoo standards were different back then), so there's just no room to add cubs we might not be able to offload when they become adults.
Secondly, even if we had the space to breed we still couldn't because our clan is a disaster. Pinduli and Moja were brought in as potential breeders after the previous hyena generation died out, but it quickly became clear that Pinduli was very much not interested. It took them years of introductions and trial and error before she could even be on exhibit with Moja, let alone breed with him. Then it turned out that not only did Pinduli not want to breed, she also had this crazy condition that I think no one had seen in a hyena before that required her to be spayed. So the new plan was to send Pinduli away and bring in Echo (the #1 ranked male in NA) and Kanzi to be our new breeders. But something happened and Pinduli's transfer fell through but we ended up with Echo and Kanzi anyway. The zoo apparently toyed with the idea of continuing to try to give Pinduli the boot and breed Kanzi, but it turned out Kanzi can't breed either (not sure why). So they just gave up, to the point that the 2020 Animal Plan said their future plan for hyenas is to only take in retirees and non-breeders, which is kind of understandable considering we're one of only two Canadian zoos to have spotted hyenas, but still a huge bummer. I have hope they'll change their mind on that though considering not everything from the Animal Plan came to pass. As much as I love Kanzi I wish they'd just send the girls somewhere and bring in a new female to breed with Echo so we could finally get those cubs.