My guess is they partnered the 3 with the greatest or reasonable money potential... the 3 partnered only have about a half dozen manufacturers competing, and market value is not likely to shrink below 50% to 60% once genericized.
They could have had Keppra but not that big a market, and Gluco which has a $ billion + market but also has about 20 competitors.
I think Ranexa has promise... let's hope it received a 10 month GDUFA date.