Intel releases have become stretched out a bit, and they do no longer renew the whole processor lineup in parallel any more. It took Intel almost a year to finish the transition to Skylake - the late 2015 iMac already has Skylake processors, but the models needed for MB Pro only became available not too long ago. The 32g ram support for laptops seems to depend on the Kaby Lake earliest - while the ultra low power versions have been released, the more powerful versions are going to be released all over 2017.