I don't understand why companies are so adamant on pushing their own streaming services, someone else already has it all setup and ready to go, pay them a small fee and you can reach a much wider audience... what's to gain by having your own streaming service and forcing people to pay for yet another, separate subscription service?
This is why people pirate/torrent.
Disney are now the biggest TV and film studios in the world. The whole point of the Fox deal was to give them a back catalogue of content for their streaming service. So while I agree with you in general, and I don't fancy paying yet another tenner a month, it makes more sense for Disney than anyone else.
Having their own system means they can produce whatever they want, without having to meet the demands of a third party. They can take things in any direction they like.
It will be interesting to see if they are willing to associate the Disney name with edgy or adult material, or if they just want to put out safe, neutral, kid friendly stuff.