In my opinion—and that's all it is (I can't state this for a fact)—the firearms industry uses a point system far more advanced than the alleged import point system used by the ATF. This is done across the board to ensure the most long term profits for each of the firms manufacturing firearms. It's referred to in academic circles as engaging in "anticompetitive practices". Essentially the firearms industry formed an oligopoly (like many industries) and each design is subjected to the point system to ensure no one corners the market and everyone competes. Every attribute is weighted and scored so that all offerings remain competitive in some way (through features and/or price).
So in my opinion, when SIG decided to go with striker-fired guns, they unnecessarily (from an engineering standpoint) designed the P320 with a higher bore axis. They probably figured they had done so well mitigating muzzle flip with the heavier classic P series this might translate enough to the striker-fired platform. By going with the higher bore axis, they can use or save their points (depending on how it works) to offer other features and/or a lower price.
When it came to the micro compact genre, the pistols are too small to shoot well with such a high bore axis, so they decided to spend their points on a lower bore axis. That's my theory.
Of course, it is important to keep in mind this is only a theory and my opinion because it is illegal. That said, many mid-level and higher corporate executives have been found guilty and convicted of this (so if you think it's a wild conspiracy theory, guess again. It happens for a fact). Virtually every industry from banking to consumer electronics companies have had executives fined or serve time for anticompetitive practices. It happens for a fact, but I can't prove it's happening directly beyond a shadow of a doubt, per se, in the firearms industry.
I think I could, however, indirectly prove it by comparing features and prices to convince a jury, but who knows. But there must be a better explanation for the high bore axis of a P320, PDP/PPQ, Hi-Point etc... HK is another one, but it works better than say a PDP/PPK because HK really learned how to engineer pistols with a higher bore axis offering hammer-fired pistols with lighter polymer frames. Most people feel a VP9 is less flippy than a PPQ, for example.
But like I said, a high bore axis is no way to go with a small & light firearm.