Software derived MSA is not a good idea. There are additives for mountainousness terrain, precipitous terrain, and other issues to take into account.
Some regulators adjust the MSA with airspace separation in mind as well.
With the MVA, you are on approach clearances, and they could be below the MSA as now you are dealing with different ROC parameters and separation issues. This also allows for ATC do give you a direct with a go-around, rather than going back to the STAR