People keep thinking that hardware power is an advantage. It isn't. From a business perspective hardware power is a disadvantage. It drives up costs.
Switch doesn't need a more powerful model to increase sales. Sales are very strong already. And if they want to increase sales then the main thing they can do to their hardware is cut the price. There are still a lot of handheld gamers out there who can't really afford a Switch. There are others who want a second one, but not at the $200/$300 price that it is currently at.
Switch doesn't even need an upgrade until they are ready for the Switch 2. What they do actually need at some point is a price cut, but even that they don't need any time soon, because Switch is still selling extremely well.