Breja: Which is one of my big problems with them - a lot of those shows feel very slow, padded and poorly paced because they don't really need to be a series at all, they don't need 10 or 12 hours to be told and it shows. It's easier to tell a story in 10 hours than 2, but that often means it's done more lazy.
Well that certainly depends on the show, and on what you consider "padding". Comparing it to books: some people find long and flowery detailed descriptions of landscapes, characters, clothes or whatever extremely boring, some don't like long dialogues digressing into stuff like philosophy or science. "Just get on with it!" :-) And others love the stuff.
Also good shows often tell more than one story at once, there's the big "main" arc, and then the stories of individual characters, how they cope and develop. Some people don't like that and call it fluff or padding, for me it's the most interesting part of many shows - because, honestly, the "big stories" have been told over and over - but there's a myriad of way people react to circumstances, how they adapt, how they deal with each other - or how they break. To show these developments, you simply need the "space".
I do agree though, that often creators run out of juice, especially noticeable in long-running shows. I guess one problem is how, if a show is successful, the publisher "orders another season".
But that problem was already there in the 80's and 90's, maybe less visible, because the number of good episodes simply decreased over time while in modern "long story" shows it often becomes obvious quickly from the start of the new season that they ran out of ideas.
"just make it however long you want and chop it randomly into roughly hour long bits"
This is actually not a thing. The problem is more "congrats, your show is a success, you will make another 22 episodes, now chop chop!" - whether there is enough material for those episodes or not.