Listing the bandwidth in bytes would be less useful because they still wouldn’t match the download rates they’re getting, but also your internet bandwidth would now be in a different format from every other networking device in your house. Paying for 125 Megabytes but your downloads only ever being 100-112MB/s is still going to prompt those service desk calls, and now going to the store and trying to buy a router would be more confusing as well because you’d want to buy one that matches the speed you’re paying for but now your bandwidth is in bytes but all the routers measure their throughput in bits and you’re right back to being confused.

If you’re streaming video from or to the internet and run into issues it’ll be harder to figure out what the problem is because your ISP bandwidth is in bytes but your video bitrate is in bits.

Changing one factor in your internet solution to bytes while every single other component involved measures it in bits is just not by any stretch of the imagination going to result in less confusion overall. You’re robbing Peter to pay Paul, but Paul is still being shorted.