As far as why you don't find Cutts in the east very often, Preston was spot in in that they're difficult to raise under hatchery conditions. Obviously, though, they can be raised in hatcheries, so that doesn't fully explain why you rarely find them outside their native range. The main reason is two-fold: A) they're far more sensitive to water quality than, say rainbows. B) They're not considered as "sporting" of a fish as rainbows are. In actuality, B comes back to A. Back when they started stocking non-native trout back in the eastern US, the primary reason for doing so was because pollution/logging/etc. had degraded the water quality of those streams to the point where brook trout could no longer thrive. Rainbows, on the other hand, were very tolerant of low water-quality. So rainbows got spread across the country to replace native fish in streams where the water quality could no long sustain the natives. Over time, rainbow trout developed a reputation as the "most sporting" trout, simply because they were the most widespread. Today, most people would probably consider browns to hold that title (that's disputable, but that's a whole other topic), but at the time when stocking was running rampant, that was not yet the case.

So when you combine the fact that rainbows are incredibly easy to raise with the fact that they can withstand lower water quality and their reputation as a "sporting" fish, rainbows got the early nod over others as the fish to spread throughout the east.