Because they can sell more views if paying customers are happy.
I refuse to pay for Netflix because even if paid I wouldn't be able to watch the content (including Netflix originals where the "rightsholders don't allow it" argument doesn't make much sense) in reasonable quality.
Meanwhile, people can watch it from an unlicensed source without paying (legality varies by country but generally low risk for users), and as long as adblock works, the experience really isn't much worse than with Netflix.
I'm all against DRMs but the friction nowadays is, if you stick to one platform, almost zero, way less than your average pirated experience.
Now, if we talk about platforms balkanization and how you have to shell out 50€-$/month if you want to enjoy just the best content from major platforms, that's another topic.
The pirated sites are often streaming sites similar to Netflix. Search for a movie, click play. Quality of service does vary, but the catalogue tends to be much bigger.
As you pointed out, "sticking to one platform" isn't an option because the platform most likely won't have the content you're actually looking for. So step 1 is figuring out which platform that is. Step 2 is probably logging in if you don't keep persistent cookies, and that assumes you're subscribed. By this time your movie is already playing if you take the "alternative" approach.
Even if you didn't mind shelling out 50 EUR/month + whatever extra per-movie surcharges Disney+ charges, the balkanization would still cause significant friction.
I refuse to pay for Netflix because even if paid I wouldn't be able to watch the content (including Netflix originals where the "rightsholders don't allow it" argument doesn't make much sense) in reasonable quality.
Meanwhile, people can watch it from an unlicensed source without paying (legality varies by country but generally low risk for users), and as long as adblock works, the experience really isn't much worse than with Netflix.