As a goalie I can tell you it's for multiple reasons.
First and foremost, protection. The modern mask is designed to deflect pucks. The players mask and cage is not designed with this in mind, it is designed to protect the head from hitting the ice or boards and the cage to protect the face from sticks. It is not designed to absorb pucks. Getting a slap shot to the face with one of those on really rings your bell.
#2 Throat/neck protection. Really ties in to reason number one.
#3 Easy to lift up. I personally remove the chin strap from my mask to make this even easier. I don't like drinking through the cage and it was also easier as a kid to hear coaches with the mask up before drills.
#4 style. Just simply looks better to 99% of the population. However there are those who still like cage goalie masks and jofa buckets.
Also a goalie and wore a cage/helmet combo most of my life. Switched to an olie cat eye only a few years ago.
When I did, I had a teammate who was an engineer for a company that did ballistics testing for CSA ( who approve all helmets/masks)
He told me that #1 was simply not true... that when the testing was actually done, it showed that on a whole, a bucket and cage combo was safer.... Problem was that by the time they had been asked to generate the data, 95% of goalies were already growing up with the new style.
In my own experience, my new style mask is definitely more durable, but my bucket was way more comfy... Less of a thunk when I catch a puck square. But if you did catch one solid, you'd be buying a new cage to replace the dented one.
Just think though... Which transmits more energy to your head/brain.... Catching one on the lower part of your dentable bubble cage, or catching one on your fiberglass chin?
I think you are right though.... The new style are better at deflecting and therefore avoiding a square shot.
Plus a new style cat eye will give you better vision.... Grid style vs grid style I'm not so sure