I wonder why some PC Engine games never made it to the U.S.?

I wonder why some PC Engine games never made it from overseas to North America for the the Turbografx-16?

I was going through my PCE games today picking out a few to play and i started to think about this.

Games in my collection like Digital Champ or Break-In to me would be "no-brainers" as we americans enjoy things like boxing or pool(billiards if you prefer).

What about Knight Rider Special,Hatris or Rastan Saga II? These games would of been a perfect fit for U.S. gamers.

Heck i could even see titles like DragonEgg! or SonSon II being released here with a few minor changes if any at all.

All of this makes me wonder if maybe if some of these great games made it here how much better the Turbografx-16 might of done?

Software makes the system right? And these games and many other PC Engine titles could of pushed the T-16 ahead of the pack but instead U.S. gamers got games like Impossimole.