Because I'm not convinced that my boys will be able to acquire firearms as easily when they are adults. Plenty to pass down and still have what I need/want for myself.
Because, There are more people in my family than just me and if all firearms are the same make and model it's easy to have plenty of replacement parts to go around, mags will fit all guns, one type of ammo and the training is universal. Also, as stated already the next generation might not be able to get their hands on them so easy.