These companies aren't operating in a vacuum. Most of their users could change providers quickly if they started degrading their service.
The reason people don't jump to your conclusion here (and why you get downvoted) is that for anyone familiar with how this is orchestrated on the backend it's obvious that they don't need to do artificial slowdowns.
Also, I just pointed out at the business issue, just raising a point which was not raised here. Just want people to be more cautious