My own opinion on why the IFBB/NPC have initiated the new classes:
1. MONEY - registration fees (plus crossovers and friends and family in the audience), pull in huge money when the number of competitors mounts up. Like any American business, the organizers are getting highly efficient at getting through a judging and evening show in only a few hours with huge competitor volume (e.g., no posing routines for most classes now). By the way, there are few "general fans of the sport" showing up at contests any more, even pro shows. So the contest organizers have become efficient at earning their money off the competitors themselves and their families.
2. LESS ANABOLICS - even though the top people in bodybuilding are into the most freaky physiques, my sense is they got freaked out like the rest of us by the excesses and experiences of the 90s, etc. I think there has been a sincere effort to reduce the juice factor through the new classes (e.g., penalize a physique competitor whose quads are obviously huge). And, oh by the way, this helps with the MONEY factor, because it opens the contests up to wider range of competitors who may not be into heavy, heavy regimens of drugs (e.g., bikini, men's physique).