Actually they can but it has to be from a proprietary account subject to the same regs as any other retail holder. That would include margin requirements, etc.
But your bigger point is correct, they cannot do so unless it is purely inventory for MM activities. Most MM keep very little inventory of penny stocks...too risky.
What a crock of bs. Just this year an MM got an fine for exactly that. So, please, do tell how they dont do it? Even further, you can only guess how many of these trades go trough without them getting caught.
"They dont" - sure. Keep telling yourself that.
The few M in $ is just a drop for them compared how much they make on doing business like this.
PS! Im not saying thats the case in BVTK at the moment though.