In a previous question, I have been told that the grip diameter of a MTB riser bar is 22.2mm. From research I did, the grip diameter of BMX handlebars is also 22.2mm. In fact, it's possible to use BMX grips on MTB handlebars. I thought this would allow to use also BMX bar plugs on MTB riser bars. As I experienced first hand, this is not the case, see picture below.
Is that because the internal diameter of MTB bars is smaller than in BMX bars?