How to encourage rolling two dice in Machi Koro?
1) If all but you gets cards that provide $ from 1 or 2 valued rolls, then it kind of does devolve into that.  Early on, get a few of those cards, but then shoot for 2 dice, and some cards that trigger on the 4 - 10 range.  You'll be able to leech off of the single-die players, but can still do your own thing.

2) play with the variant where not all cards are available at all times.  

3) The expansions add even more cards to the mix that allow #2 to be even more feasible