Has he been able to shoot any of the pistols in question or at least fondle a bunch before the purchase day? Or will all the fondling happen on the purchase day? If he has shot or fondled already, what's he say?
Personally, I think the opposite could be asked, why not a Glock over the others?
For any model, metal or plastic, maybe he likes the ergos and trigger or looks better. I would say there is some benefit to the Glock in it's simplicity for a first pistol. However that feature is not unique to Glocks.
I think my g34 is a great range pistol, but so are my 1911 and 226.