This theory doesn't make a whole lot of sense. If it was a sales concern Capcom would be more concerned about the bold new MH title that cost a lot of money.
And with so much of the MH market being Japanese handheld players, porting World to Switch would allow for a safety net.
The real reason is that MG Worlds targets 30fps on superior technology to the Switch, and that's IN dock mode. It would take a lot of R&D to get it up and running.