WHY? It's only been the last 15-20 years that the size of the avg cruiser has gone up over 40' or so. A generation ago people were out there in boats in the mid 30 foot range. ....
I personally don't want something bigger than 40'. And I'll be glad to go offshore in something smaller than 40'.
Older boats were a lot heavier and a lot slower. An American 30 year's old 33ft will probably weight as much as a modern European 40ft big production boat and, if it was built now, would probably cost about the same to produce.
There are exceptions, but as a rule, to have the seaworthiness of an older smaller boat you need now a bigger boat. So for the same money you have a bigger boat, the same seaworthiness, lots of more interior space and a lot more speed. It makes sense to me and it seems that to most sailors. That's why the market has moved in that direction