None of these big tech companies really need to grow bigger. The smartphone is essentially done. AWS just prints money. Social/consumer apps are "done". What more is for them to do but collect rent?
The US government needs to break them all up. That'll oxygenate the entire tech sector, unlock value for investors, and kickstart the playing field for startups.
Google, Apple, Amazon, Meta, and maybe Microsoft. Break them up.
I'm struggling to think of a part of the OS that hasn't had ads shoved into it... the terminal I guess... There have been ads in the start menu, the lock screen, in pop up notices, in the file explorer, in search results, in the control panel, on the task bar, in the share pane, in windows update and in a bunch of windows apps like ink workspace. They've even just force-installed random programs to people's systems.
I'd wager, too, that the addition of the garbage you're describing has coincided with the OS's worsening performance. File Explorer performance is so abysmal that it may as well be an Electron app.
On the other hand (edit: regarding your first paragraph), Microsoft seems very serious about not falling afoul of the law, probably because of the cost of the anti-trust litigation they faced in the 90s and 2000s(?). It wouldn't surprise me at all if there were nothing for a whistleblower to blow the whistle on.