If you invested $200,000,000 into a product that had no foreseeable way of being consumed by the public through the medium it was designed for, you'd price it accordingly to get a return on your investment too. Arguably they can reach more people with Disney+ than in cinemas, but people aren't used to paying for a new release movie so the pricing is going to be variable for a while until the market dictates where it should sit. Same as it did with music streaming vs paying for individual tracks vs buying a CD, and other streaming services in comparison to physical media.
I think you'll find the other studios looking at this to see how it pans out. If successful we'll see other studios releasing first run movies online. A lot of theater chains in the US are not looking good financially thanx to Covid and other things. The studios in the US have now been allowed to buy theaters again to stop them from going bankrupt something that was banned in the 1950s.