There's a bit of math missing here: Disney isn't taking 100% profit on this money...
The breakdown in this
linked article suggests that while its D+ service is indeed popular, there may be opportunity costs that are reducing the net impact for Disney (55% increase in one sector, but a 3% increase overall, in a year with buckets of inflation, tells you something). You might reasonably surmise that D+ is supplanting rather than supplementing in-theatre viewing, for instance, making the whole movie making endeavour less profitable overall. But ah well, I'm a firm believer we should be entering a phase of shrinking corporations and Disney's got to shrink...