We'd have to invent a new connector first. It's too thick for modern laptops, not to speak of cell phones.
Also, RJ45 is terribly fragile if you keep plugging and unplugging it, eventually that latch will break. And copper can barely support 10G and is terribly power hungry when it does that. And the cables get thick and inflexible.
Lenovo has re-invented this particular wheel to fit in laptops, some ThinkPads come with a proprietary Ethernet port which is around the size of USB-C, just with Ethernet signals. And you can get a passive breakout adapter to convert it to RJ45 (idk if it's included with the laptop).
https://www.lenovo.com/us/en/p/accessories-and-software/cabl...
The 8 pin modular connector as found in most ethernet does have several sins but it has one huge redeeming feature, A feature I wish was found in every cable. It is easy to field terminate. Have fun putting a new end on nearly any other cable.
Field termination is necessary when the connectors are too large to pull through a conduit. But if they were USB-C sized, you could just pull fully assembled cables.
It also comes in very handy when you need a 8m cable, but only can buy them in lengths of 5m and 10m, or when you’re wiring an entire building, and figuring out which lengths to order up front is a major pain in the ass, certainly compared to ordering a few hundred meters of cable, a few hundred connectors and tools to put the two together. And that’s ignoring the price difference.
It’s also about managing length and slack.