You're not wrong, but you're also not 100% correct.You still have the issue of asking folks to pay up front. If you want to pay up front for several seasons (a "complete story"), we are talking tens to hundreds of millions of dollars for a premium TV show. That's.. a very large investment for crowdfunding.
And, now that you are adding a sense of entitlement - what do you do when folks start saying, "I didn't pay for the story to go in this direction! I didn't pay to see my favorite character die!" or what have you?
You're making a slippery slope argument. Making sure they plan an exit strategy is not the same as guaranteeing everybody will like the story.
Stranger Things demonstrates that they can write and film a complete season that completes a story and still leave threads for another season.
Babylon 5 demonstrates that you can plan the entire series, not just a season in advance, and account for actors leaving and changing networks. Even if people didn't like the last season as much. Mission accomplished.
The OA was largely unresolved in a huge cliffhanger. Exciting, but why would I advise any friend to watch it, knowing that its incomplete.
TV Land is littered with canceled TV shows. It's not a new problem. But the world has changed and now we pay directly to the producers. Maybe we ought to get something for that.