...yeah I know this is belabored beyond belief; but I thought of another handwave for ya'll to use that I don't recall reading on these boards:
Planets can only form in stars with a high enough metal density. Such stars can only form in highly active regions of gas and dust. Such regions are basically rare to far north and south of the galactic plane. Even if there are worlds to visit there are too spread out even for J6 drives with extra fuel to safely visit. Thus a relatively flat galaxy in terms of viable star-hopping.
Is there a consolidated list of potential handwaves?
Planets can only form in stars with a high enough metal density. Such stars can only form in highly active regions of gas and dust. Such regions are basically rare to far north and south of the galactic plane. Even if there are worlds to visit there are too spread out even for J6 drives with extra fuel to safely visit. Thus a relatively flat galaxy in terms of viable star-hopping.

Is there a consolidated list of potential handwaves?