I understand injuries happen in training but I have a hard time thinking of why you would break a hand in training other than throwing too hard with small gloves. It just seems like a very avoidable injury.
What are your thoughts on the matter? 
Galanis -Yup.
It's the opposite of avoidable.. It's by far the most common injury in all combat sports. Definitely not due to bad training. All it takes is one shot to land the wrong way on someone's skull.
You're throwing 3/4 speed and your training partner lowers their head and you catch them just above the forehead.
Or you catch a knee, elbow or the top of someone's head in a scramble.
I've done both and neither was unsafe or reckless training.
Even with thick boxing gloves on if you punch somebody in the elbow or something like that your hand can easily break 
He was practicing the longo "punch a fucking hole in his chest" move.
unlucky mostly.
Pitbull3744 -Haha Gladiator ruled. When Dennehey launched Cuba Gooding Jr out of the ring with an uppercut I almost shit.
Pitbull3744 -VU
Shit happens. I broke my hand rolling no-gi but never hurt it while striking.
Maybe maybe not.
I broke my hand with 18 oz gloves on upper cutting someone like half speed. Was the weirdest thing. Pinky took all the force and shattered