It’s down to money really. Lotus seem to have the most, so they have more chances to give KERS a try than the rest. If they try it on this year’s car as well, they’ll have more time to debug it ahead of next season.
As for the rest, if HRT has enough cash, Frank may be convinced to let their Dallara use his lowline gearbox & KERS system, while I doubt that Virgin can use a Mercedes sourced KERS…