It's all down to self interest.
The ALMS has attracted the manufactuers, the best US and European teams (for the blue ribbon events), top drivers, and been run in a thoroughly professionally manner, with great TV and media coverage.
The LMS has always attracted large grids, but let's be honest, you guys over the pond have always looked down on the series as second best, and quite rightly so.
The introduction of the LMIC is attractive to the very manufactuers the ALMS want to attract, that's were the self interest lies.
I'm all for the ALMS, but not at the expanse of ACO racing in Europe. If ALMS fans want Audi to return, let Audi Sport North America fund it entirely, or have a set-up like Champion and the R8.
The only time the factory Corvette team venture into Europe is for Le Mans, the rest of the time they are represented by customers.
ALMS fans have had the best of both worlds, the LMIC throws a spanner in the works.