"Short" in this case may mean a few years. Compare with SpaceX's test communications satellites, with a lifetime of six months: https://space.skyrocket.de/doc_sdat/microsat-2.htm

Lower orbits are cheaper to reach, and just like cellphones the high turnover of technology means that they will become obsolete quickly too. Today you might want a ""5G"" base station in space (+), in a few years time you'll want a ""6G"" one.

(+) this is an analogy