Question about moose?
"I thought moose were like the size of deer [sic]" They are the size of deer because they are a species of cervid, i.e. deer.
moose are larger than deer
It's because they're basically unchanged from caveman times. Out of all the large species from prehistory (cave bears, cave lions, wooly mammoths), moose just happened to survive, probably because they're hard to kill.
Because all the little meese were killed by Boris and Natasha.
What kind of answer do you expect? Their size is their size.