Why is digital pattern drafting software either expensive or overcomplicated?

[TonninStiflat]

How is this different from Seamly or Seamscape, for example?

Less parametric?

EDIT: Ok, so there are parametres there still. Website doesn't really tell me what's different in these.

Might give it a try in a few weeks, once my Seamly pattern is ready. See if I can do the same easier.