From memory, one of the limiting factors is entry-speed into the ramp, largely through nose-gear limits - which also affect the profile of the ramp. That basically means that end-speed of any cat is limited to that entry speed for the ramp. What that means is that any cat ends up being provided to accelerate the aircraft to a relatively low speed, so all you're doing is replacing a long flat deck run with a shorter one, enabled by a system that adds quite a bit of cost / complexity. The fact you're using a system also means that you end up slowing down launch rate (to allow shuttle return, line-up, aircraft hookup check etc. Duplicating that system for redundancy or increased launch rate will be problematic, given you have to align with a single ramp. You might get some extra safe parking deck area out of it, but not sure it's worth the effort and cost.
Significantly reducing the ramp angle means you'd end up with higher end speed and a longer cat, albeit potentially easier to include multiple ramps/cats, but it's still a marginal benefit, if any.