They could double the power of the Switch GPU just by replacing the current Tegra 1 that's inside it with the Tegra 2, but they won't do it unless and until the Tegra 2 costs the same as the original Tegra 1.
It's all about the bottom line with Nintendo, nothing more.
The Switch doesn't use a Tegra 1, it uses a Tegra X1(The 6th full-power Tegra chip). The Tegra X2(Which I assume you're referring to by Tegra 2) is not in any way a replacement or upgrade for the Tegra X1, given it was intended for automobile applications, uses a completely different CPU architecture, with fewer cores, a different GPU architecture, a significantly higher TDP(As it's not intended for mobile use), while generally offering minimal, if any(Depending on configuration) performance improvements for this application.
NVidia hasn't released a new mobile-orientated Tegra chip since the X1 used in the Switch(Because every single one has been a commercial failure with few if any design wins up until the release of the Switch). There is no "drop-in" replacement for the Switch's SoC. All Tegra's since have used custom CPUs intended for many-chip scailing. Chances are, the replacements will almost certainly have to be custom designs, in order to improve performance while maintaining compatibility, unless Nvidia decides to continue their expensive and loss-making Shield line as a halo product(Though even then, NVidia can't make another portable device as a result of their contract with Nintendo). There is no other commercial electronics device on the market using NVidia Tegra chips anymore(Since the release of the Shield TV, pre-dating the Switch significantly), with the exception of those embedded in certain high-end cars.
With all due respect, you don't seem to know what you're talking about, with the exception of acknowledging that every for-profit company operates for-profit. (Although it's worth noting that Nintendo, like every other manufacture up until the start of this generation, predominantly sold their hardware at a loss. No manufacturer of consoles still actually does this though, with Sony likely having the highest margins of any).