Because each of them are charging you $15-$20 per month to access their platform that realistically only has one or two things that actually provide you the value for what you spend.
So now, instead of spending the $100 or whatever it was with your cable TV company to get access to all those channels (which, while you couldnt pick what was on when, they were all included together), now you have to spend like $150-$200 to be able to access the same kind of content as before.
And to make it worse, you used to be able to buy a Laserdisc/VHS/DVD/etc of a movie you really liked. One time purchase, not a monthly subscription. And you didn’t have to think about what youre going to do when the streaming service decides to remove your purchased content from their servers (spoiler alert, they almost never will refund you or give you a copy, it just disappears along with your money you spent to buy it).