That was a huge pet peeve of mine back around 2006 or so, when I was still buying movies on physical discs. Apple never put in a Blu-ray drive on their machines. I waited, and waited, and waited, but it never happened. Maybe they didn't want to pay the licensing fees, or maybe (I feel this is more likely) they wanted people to use the iTunes Store as their sole source for movies instead.
Luckily, today there are plenty of external Blu-ray drives around in the under-$100 range.