I don't really understand the time line. How can it take 4-ish years to construct a satellite? It’s a modular platform they’ve been building for over 25 years.
We construct and deliver two Virginia Class Submarines in that amount of time. I bet the basic platform is constructed ahead of time and is waiting for a final decision on the broadcasting equipment. There’s got to be a lot of time spent waiting, otherwise how could it take 4 to build?
Re the timeline - it doesn't take 4 years to assemble a satellite presuming you have all the parts in hand, on the cleanroom floor, at the time you start building, and presuming you take the absolute minimum time to verify and test and certify each production step along the way. However none of those presumptions is accurate. I would bet a good deal of money that "manufacturing start date" is a milestone that matters about as much as "laying the keel" on a battleship (e.g., "not very much.") Weld the first two members of the bus spaceframe and you've "started manufacturing."
As for comparison with your subs, I'm pretty sure your employer has a much bigger budget to work with, along with the attendant logistical supply chain infrastructure, than does any satellite manufacturer these days (LMSC may have had comparable resources to work with back in the day during the heyday of the GAMBIT, HEXAGON, and Keyhole programs). Furthermore, your boats get sea trials and periodic refits and port time - once a comsat goes up, that's it. It's gotta work right, the first time and pretty much every time, for 15 years, without servicing, physical upgrades, repairs, refits or replenishment of consumables, 22,300 miles from "port."