maybe if cops spent more time on firearms training this wouldn't happen.
and why would you regularly a glock with a round chambered?
This is finally an explaination of the "kaboom" phenomenon, over-attributed to Glocks (note that Sigarms issued a "don't do that", implying the same issue).
This is common behavior, "clearing" it for assorted safety reasons then loading the same ammo later (entering & leaving a cold range, storage, air travel check-in, interstate ground travel, cleaning, etc.). Often will use one kind of ammo (possibly quite expensive) for carry, and another for practice (possibly quite cheap), and load the same ammo in the same mag repeatedly - as the carry load is not often used, a few rounds may get chambered repeatedly.
When chambering a round, the mechanics of chambering can compress the round. Apparently it doesn't take much compression to cause a significant increase in pressure. This is magnified by serious defensive needs leading to use of extra-powerful so-called +P or +P+ rounds, which are straining the limits of safety already.
why would you regularly a glock with a round chambered?
You're missing a key word there. Presumably it's "carry".
It's perfectly normal to regularly carry a Glock with a round chambered: pull trigger, go bang - just what you expect. If you need that bang, you don't want to waste time fumbling around with chambering a round. Also, it gives you an extra round (X rounds in the mag, plus 1 in the chamber).
Department regulations would be one excellent reason. Another is having attended the funeral of a pal who had carried his handgun with the chamber empty for *safety* reasons.