The thing with SP's Alps sets is that they don't have any tapering on the stem (chamfering, I suppose) like original Alps-made key sets have, and on top of that, DSA also has a much longer stem than usual which makes pulling out a PITA, all analogies considered. Seriously though, the stem's lack of chamfer and length makes them fit very, very tightly.
There have been two recommendations I've heard from the community:
1) Remove all flash molding from the stem by inserting and removing it from a switch
2) Add chamfer to the stem yourself with a tool of some kind (x-act, dremel).
That claim by Matias certainly sounds a bit dubious. Also, Alps wobble isn't that bad. If you want bad wobble, try Gaterons or Zealios.

Here's the chamfering detail from original Alps-made PBT caps.
Even some old Alps keysets fit tightly though, and in my experience. I've had caps fit tightly on one board but loosely on another. I'm not sure if this is simply differences in tolerances between sliders/caps or a loosening of the slider's mounting recess, but there is some variance in terms of fit when it comes to geuine SKCM/SKCL Alps.