Above all, Apple wants to show that their hardware is awesome, especially because it really is. Running x86 games or compatibility layers even with great emulation will make that $3000 Mac look half decent at best, against a $1500 gaming laptop. Simply not the story Apple want to tell.
If they stopped restricting the iPad, those people would only have to buy an iPad.
And as someone without a single interest in an iPad, I would worry that removing the iPad limitations would increase its market-share and lead to Apple reducing even more their interest in the MB, which would be terrible news to me.