Easy - Netflix. You might remember a while ago that Netflix (using Level3) would be throttled by many providers resulting in a lousy streaming session. This was often worked around using a VPN service as it was discovered Level3 traffic was often being routed to a singular network port even though other links exist .
https://arstechnica.com/tech-p...
Verizon did the same a few years later - routing all of Level3 through a 10Gbps port.
https://www.zdnet.com/home-and...
Again, a VPN solved the issue.
Now, after that, a new threat emerged as mobile data started taking priority - zero rating. That is, you could watch streaming video from a few "select providers" without it impacting your data. T-mobile was a big promoter of this and offered many services (like Netflix) for free, while forcing other providers to use your data plan. Land based ISPs started doing similar things - providers who paid for the benefit found their traffic zero-rated and not counted against bandwdith quotas. This was seen as an end run around the issues mentioned earlier when ISPs wanted to bill Netflix for their traffic. Now they could bill Netflix for their traffic, but wrap it up as a "promotion" where Netflix traffic no longer counted towards your monthly 100GB transfer limit. Some sneakier things also included moments of "bandwidth management" where because Netflix paid, they'd get full bandwidth, but a provider like YouTube, who might not have paid, now gets throttled so while you could get 1080p on Netflix, you'd struggle to get 480p on YouTube, as a "help" to save your quota.
You generally don't hear of such things anymore, mostly because they were illegal, then not illegal, then illegal, and likely currently not illegal. And you certainly didn't hear of Verizon or Comcast going bankrupt because of it.
Instead, what happened was everyone started figuring out new things, like bundling services together - where you could subscribe to Comcast and they'd give you streaming services for free as part of your monthly fee.
But the purposeful mis-routing of traffic, or zero-rating stuff, doesn't happen anymore. At one point there was talk about "fast laning" traffic - certainly providers could be made to load faster - if you were a fan of news, certain news partner sites would load really fast - so you'd buy basic Internet, then subscribe to news like a cable package so you could visit CNN, Fox News, etc., much faster than normal. DInky local news sites need not apply. Or perhaps you'd purchase "Social Media" where you could do Facebook and Twitter as fast as you wanted. But has-beens like MySpace or Second Life, forget it. That never materialized because it was so obvious what was happening.