I think you underestimate how much they hand out Disney+. For example, Verizon has a deal with Disney to give out free Disney+ with many plans. Comcast, I think, was also offering me free Disney+ access. This must eat into margins on some level while keeping the subscriber number up - there's no way that Verizon/Comcast are paying full price for that free subscription (in most cases, it's only a year free).

Contrast that with HBO Max that has never had a sale of any kind except for a single free trial week.

I also think that people underestimate the cost of serving streaming entertainment. It's very compute- and data-intensive. If you architect your systems badly, which I assume Disney did, you will be paying a LOT of money for this service.