The original tends to have a certain magic that makes it work so well. Whenever you remake something there’s the risk that the magic is diluted, or lost completely. It’s extremely rare to add more of what makes it work. Sequels often suffer the same problems.

Basically it’s not that remakes are inherently worse, they tend to be more average. It’s just that studios don’t remake poor shows. So we tend to see a lot more of the decline.