I was a Homeland fan right from the start. Great performances, constant suspense, smart developments. The show remained watchable in later seasons, but the amount of action was greatly increased. Previously smart characters became dumb, and on season 7 Carrie Mathison was more action hero than spymaster.

Most recently, this is happening in Amazon's series Jack Ryan. The first season was a good thriller with interesting twists. The second was basically "Jack Ryan: Navy Seal". We know right from the start who the bad guy is, and, in the end, we get a "twist" that is both lazy and predictable. Not only that: Jack's "cowboy" behavior gets absurdly dumb (he's kind of an asshole too...), in a way that is not compatible with his backstory. I won't spoiler anything, but in this season he does things that would make Jack Bauer stand and applaud.

To me, that's frustrating because I love all that spy shit, preferably with large doses of realism. If I want action I'll watch Mission Impossible or something.

One of the possible reasons for the increase in action scenes in successful spy shows is the larger budgets. They start small, with character-driven stories, and grow to be action movies.

Another might be the need to please and retain a larger audience gained in the first seasons.

They also tend to get less and less realistic, like The Americans.

I wish there was a spy show that kept being a spy show all the way through.