They didn't "get tired", they found rich soil and ample water to do farming and milling, which is what they were intending to find. It's called the bread basket of America for a reason.
Wasn't it just that it wasn't yet settled, so you could settle there and claim some land? That implies that Indiana or anywhere else on the way would have been at least as desirable, but someone else got there first.
Source: I lived in Nebraska and Indiana.