The reverse is the case. Longevity of satellites had increased over time. This is due to a variety of reasons ranging from materials and design improvements to more advanced electronics and superior stationkeeping thrusters as well as reduced reliance on consumable components.

Early spy satellites, for example, relied on film that was returned to Earth, once the film ran out the satellite was useless. Other satellites simply became obsolete or lost attitude control and were no longer useful. Telstar had a service life of only about a year, the first half dozen TIROS weather satellites had lifetimes of about a year or less. Today satellites with similar missions are expected to last decades, which they often do.

Another reason is that nobody is detonating nuclear bombs in space these days. A major cause of Telstar's short life was intense radiation from high-altitude nuclear tests. I'm not sure how long it would have lasted without that....

Hah, well, that only happened once. And even so the overall lifespan of satellites was not very long back then.

Yeah, I definitely get the impression that Telstar might have lasted two years instead of one if not for the nuclear tests, but not decades.

I very much doubt anyone would consider something that costs hundreds of millions of dollars to build and fire into space "disposable". It's not like you can buy a new one for cheaper 5 years later.

No they wouldn't launch a spy satellite disposable camera that took one roll of film and was then useless after the film was jetisoned.

https://en.wikipedia.org/wiki/Corona_%28satellite%29

They are considered disposable because the operating costs usually outpace their value once obsolescence sets in.

Which is why many satellites are resold on secondary markets after their primary mission timeframe has passed.

Well, you sort of can. The majority of cost is R&D, once that's done and you have a template for a satellite, you can definitely build more of them cheaper than the first one.

How about Rosetta?