I think you hit the nail on the head when you mentioned the uncertainty these productions face from season to season.

I think public perception directly influences the future of a TV series, even though it has already been fully shaped by its creators. This is where major studios can ruin everything by focusing solely on money.

It would be a difficult and heartbreaking task to write the end of your own job. Thinking about it that way it kind of makes sense that the quality can drop off a cliff when they know the end is near.

It is precisely for these reasons that the ending must be the first thing considered in a TV series.

Not to mention wrapping up multi seasonal plot lines that you've planned on continuing. That alone would be a huge problem.

This can easily snowball out of control and never yield anything positive.

If this scenario does not change over time, the audience may increasingly turn away from this type of audiovisual material.