I admit I don't know much about how chip production works, but I'm unsure if it's as simple as just taking the current Switch lines and turning them onto making Switch 2 instead.
If it is that simple, then I can see them cutting Switch production off very quickly to get the successor off to the best start possible.
On the other hand, if not all their current lines are capable of making the new chip, then it might make sense to keep churning out a small number of Tegra X1s for another 2-3 years so that they can keep a budget option on the market for lower income consumers.