There's something called a flash drive ....
... which is slower than gigabit ethernet, usually.
Seriously, it's faster to copy files between two computers by using ethernet than it is to copy the files onto a flash drive and then off again. Much faster. Heck, it's faster to copy the files than to do either of reading or writing, let alone doing both in series.
As to whether it makes sense on a laptop: Not every feature of a laptop has to be in use 100% of the time to be worth having. If I have a dock of some sort, obviously I'll always use Ethernet, and I probably don't care that much whether or not the laptop has the port. But if I go in to the office (I normally don't, it's 1500 miles from here), I'm going to bring a laptop, not a desktop, because carrying a desktop on a plane would be silly. And when I get there? I want ethernet.