In-universe, historically, we have 15-light-year KF drives as the eminent jump system. If you look at a map of the inner Inner Sphere, 15 LY jumps tie you down to specific routes to a large extent if you only use settled systems; for example, about any route from Terra anti-spinward - and there's a large number of early colonies there - would run via New Earth.
One could also deduct that the early spread and ubiquitous installation of recharging stations specifically along such routes - read: about every settled system in the early colonization phase - means that these routes were also used predominantly for shipping; that other avenues - unsettled systems or interstellar medium, even non-standard jump points in-system - tended to be pretty much a negligible factor can be seen largely in the fact that canonically, troop convoys are attacked at known jump points throughout the next millenium.
