Yeah it's probably not a budget thing. Thinking about it further, I wonder if it's due to them not wanting to have a figure covered in pegs and holes.
It may even be a directive from Hasbro corporate about not going against the established universal play pattern, which is 5mm ports.
Also, the designers have hinted at wanting to redo minicons down the track and so those may have a flip out 5mm peg, rather than a traditional minicon port.
I know none of this is going to satisfy anyone, but just my thoughts on what may be the case behind the scenes.
Looking to buy lucky draw Armada Prime and Diaclone Marlboor Wheeljack.