But from Netflix's end, this wouldn't really be about new subs and/or retention.
(Although, one could argue that it's good advertising and may actually produce a small bump in subs. On top of that, creating a bigger brand identity for something like ST is always a good thing.)
But I digress. This would be about a cash-flow to them. Uni would be on the hook for an initial licensing fee and, likely a small chunk of merch sold, depending on the contract.
It's a win-win for Netflix, and I would have to think not doing ST would be a UOR decision, for whatever reason.