1/ Scientists only investigate what they are paid to investigate.
2/ Type 2 is historically viewed as a self inflicted disease.
3/ The small number of T1's is (was) relatively easy to mange without ploughing billions into finding a cure.
4/ Cost wise, diabetes has until fairly recently, not placed much of a burden on the health system in comparison to some other diseases, cancer for instance ( - which affects 1 in 3 people statistically).
It is now recognised that whilst T2 may be the result of lifestyle choices for some individuals, there are many for whom lifestyle is not attributable. Over past decades, billions have been spent on cancer research and I would suspect that the money being spent on diabetes research is almost insignificant in comparison.
With the prospect of diabetes becoming global issue where the number of affected people is growing exponentially, we will see more funding going into the research and hopefully we'll see some benefits in the coming years.