I don't see why someone would do this?

Where oh where did I see this before???

Some breakers would allow 2 wires under their screw but they would have to be same size wires. This just looks like a bad job.

#12s under 60a CB=really bad. At least they used number coding, prob. panduits to make it look like a swiss watch too. I guess it could be a tap rule....

isnt that the way emon meters are often connected

Might be the way, but it is a violation unless the brkr is listed for two. Like SqD for example
E- mon requires OCP on voltage conductors

Each breaker was serving 2 different pieces of equipment in the first photo.

I think even the Sq-D breakers aren't listed for 2 different sized conductors, as in the case of the first photo.
(E-mon meters require a 1/10th amp inline fuse on the line side.)

I don't see anything on the label that implies the QO breaker can only accommodate one wire size.

It says "1 or 2 AL/CU #8-14"

One comment I heard a while back was something like.....

"I'm using the <10 foot tap rule! The small motor only draws 7 amps, so the 60 amp is still not overloaded"