You are always taught to keep the outside arm free from contact if you have contain, as Mack would have on this play, so he was only able to engage with his left arm. Hence why its in the centre-line, he can’t get drawn into a 2-arm (4-arm) grapple. So its kind of a consequence rather than by design.

I agree that I doubt a smart GM sees IT as something you want to tie your wagon to.