Why bother making a “main product” at all

My guess is legally protecting themselves against potential new laws and regulations, so they have more time to make changes or continue making money if these practices get outlawed.

Why is this exclusive to the mobile market?

It’s not; it exists in computer and console gaming too, just to a lesser extent. As to why, my guess here is that mobile has a lower barrier to entry, and they’re always accessible where a computer or console might not be. There’s probably some sort of “cultural” aspect here too, where it’s already prevalent in mobile so people are more accepting of it, but computer/console gamers had their own culture where this didn’t exist for many decades and so won’t be as accepting.

That’s basically what the Pixel 7 Pro is over the Pixel 7; it’s just that it also comes with other extras, like another camera.

Not sure why they only managed 14% extra battery in the 7 series though. It’s the smallest jump from their smaller model vs the larger one except for the 6 series. Combine it with the more power hungry display on the Pro, and the already-inefficient chipset on both devices, and you just don’t get the battery life that competitors get.