In my expierence most teams don't have great passing and offensive flow so their team doesn't get many assists.
Also, a lot of teams play outside attack tactics rather than inside attack tactics and in my opinion/experience you get more assists for players when you play an inside oriented tactic.
I believe you're right and in fact I have been thinking about this.
My hypothesis is that it is more complicated to compare the effect of passing compared to most other skills. For instance your rebounding can easily be compared with the oponents rebounding in order to calculate the likelihood of getting a rebound. Likewise for inside defense compared to inside scoring and so on. But, passing is harder to analyse and therefore people can't valuate it and choose to go for players with skills that they "understand".
The consequence of that of course is that players with passing skills becomes less attractive then they should and therefore less frequent as you say.