Why is a human mouth known as a piehole or cakehole?

Just the generic term for savoury/sweet produce that can be shoved down your neck.
Personally I say “shut ya gob!”

Cos it is a hole where one puts pie or cake (depending on preference).

I prefer pie or cake to sushihole! :-/
‘shut your sushihole you sushi faced eating bast*rd’…. Doesn’t have the same ring to it :-/

Just an example to get the point acress. Perhaps because pies are the food weapon of choice to be shoved into people’s faces.

There is an interesting discussion of the topic here

Because it has a somewhat nicer “lyrical” ring to it compared to “cake” and the word is quite common as well, so it is easily understood.

Compared to when you yell, “Shut your burritohole!” or “Why don’t you just shut your dimsumhole?!”

I thought maybe it was a dated phrase… like, back in the day, people ate lots of pie. However, I like Urban Dictionary’s answer:

cake-hole
Noun. Mouth, i.e. the orifice one ought to be using for eating cake rather than talking shit.