I spoke to a guy last week (mid-way through B737 endorsement for
VB) who's been flying B767's for umpteen years overseas. I'm also heavy-jet endorsed with multi-crew time as well. Therefore if lack of multi-crew time dictates that you go on the B737, I think we've just blown that theory out of the water.
Honestly, I think it's nothing more than HR looking at a pile of candidates for the month's interviews, and putting half in a box labelled "Boeing" and the other half in a box labelled "Embraer."