Satellites have lots of components, so even a “very basic” satellite would take some time. Also, most satellites are tested lots, sometimes on a practice model, as they cost lots and it’d be terrible to launch something that doesn’t work.
Our telecoms satellites are al very similar, which means we know lots about them and they don’t need to be analysed and tested as much. They take around 3 years from a customer saying “I want one” to when they are launched.
In comparison, most of the science programmes are really specialised so they can take 10 years, if not more!