Hi, you can read about 64bit requirement or example here or here
I think there is no only one answer, it happens already on other platforms like mac, seems 32bit will be deprecated. Was necessary adopt this requirement else mdosbox development would be stopped. We can be happy that M-HT is genius and 64bit dynamic recompiler is not slower then 32bit. Except that requirement was none reason for making 64bit binaries. Google says 64bit is faster because offers more registers, but who knows.