Errrr, yes, but that's for a 10/100 adaptor. Try looking for USB2 gigabit adaptors (eg here, and you'll find that (a) the apple price is actually pretty good and (b) obviously the USB2 ones are going to come up short on bandwidth, especially as USB isn't full duplex.

Apple are obviously making out like a bandit on their old USB-ethernet (though less than you'd imagine, as I'm 100% sure they will be CNC machining that plastic after it's moulded to make it more aesthetically pleasing), but I wouldn't be surprised if they are only just breaking even on the thunderbolt-gigabit one. There are likely at least two ARM processors in that cable, plus gigabit magnetics, MAC/PHY, and probably a thunderbolt<>PCIe bridge chip... all packed onto a very small board that'll be expensive to make.

As for "easyjetting", Apple worked out that most people don't use wired ethernet these days, and so dropped it - just as they dropped optical drives. I admit to still ripping CDs every few months, but I only use ethernet for some rather specialised use cases, like bridging a USB LTE adaptor to an external wifi router.

I'd honestly be amazed if 2% of MBP customers used ethernet once a week or more.