All plastic gets brittle with age and subject to breaking, or flat crumbling, at any point. The injection molds are kept going 24/7 turning out this garbage and disentegrating plastic is a way of life.
One strives to avoid breaking it but sometimes it happens no matter how much care is used.
You should see the inner fender plastic on the old Merkurs. It’s 3/16" of an inch think and can be crumbled between the fingers like a regular potato chip.