Why? (Genuinely curious if there is a reason, I'm not an expert on this)

Satellite-to-satellite connections are handled by pointing lasers at eachother. Ground-ground connections are handled by pointing lasers at eachother through a fiber. Fundamentally they seem pretty similar to me.

I wouldn't be skeptical about the bandwidth, I would be skeptical about the execution. There are existing inter-satellite links, but they are far lower bandwidth. You need much more precision and signal processing at higher bandwidths.