sv.memo.cash uses SV blockchain/protocol and now has 65000 characters limit, because the BSV guys who want to remove all artificial limits, started doing so already, and this is one of them (I think its called OP_Return limit, I think they increased it to 100KB), while the memo.cash still uses the BCH blockchain/protocol which has much smaller character limit (I can't remember now, but I think its 256 characters or something like that).