The tall cans have more surface area. It does mean slightly more materials (but not that much because the can thickness is not uniform), but also more visibility in vending machines and stores. It’s a purely marketing decision.

They have very, very different business models. Constellation size is meaningless on its own, you have to account for the satellites capabilities, orbits, and the number and needs of your customers.

This is true at 500km altitude, but not so at higher LEO altitudes.

It’s a way for russians oligarchs to get back to their frozen assets.