In contrast to many other states, missouri, kentucky, and maryland had a difficult time deciding which side to join during the civil war. why do you think this was so?

They were all on the outskirt of the two sides and every one of them had motivations to go both routes in the contention. 
Maryland was a slave state and from multiple points of view held to an indistinguishable thoughts from the Confederates. The most compelling motivation that they went poorly them is on the grounds that the US government ensured there were a lot of troops there, so Washington DC wasn't cut off amidst Confederate land. 
Both Missouri and Kentucky had their own smaller than expected form of the Civil War going, where neighbors battled with neighbors.