Why does every satellite have to be custom made like this? Without knowing anything about it, it seems as though most communications satellites do pretty much the same thing?
They aren't built in very large numbers. There are maybe a couple dozen commsat launches per year, and they do have fairly different requirements a lot of the time. There are variables like frequency, spot size, transmission and receive power, and whether the satellite does any on-board processing or routing or whether it just acts like a "bent pipe." There is some standardization, but not a whole lot. Economies of scale just don't quite kick in enough yet.
Superficially maybe, but you want to send zero weight you don't need into orbit so it makes sense to build to the exact mission profile vs trying for a generalized solution.
There are many standard components, though satellites are low-enough volume that almost nothing is really "off the shelf". The custom bits and integration are plenty of work (and time) in themselves.
Also, we really don't want to have all the communication satellites to have the same bus, and find out years later that they have some bug that causes them to malfunction after years in orbit.
To a degree every satellite is custom because of custom requirements. To the extent that they're not they can use an existing platform, like Boeing does with the 702.
