They do. The 5700XT is still an excellent card, the 6700 and 6700XT are coming out soon, and the 6800 and 6800XT are both absolutely killer cards as well, especially at the reference prices.
Vendors and demand have effectively driven prices to an insane amount, and you just can't get them, unfortunately. Short of AMD doing something like Nvidia is doing here, I doubt we'll see them on store shelves any time soon.
AMD already did this. The RX6K series are terrible cards for mining. The radeon 7 smokes the new cards because the new ones where designed to be as bad at mining as possible without effecting raster performance.
RX 5700 will hit 55mhs and the RX6K series will do ~68mhs, but the cost of the 5700 is typically like half that of a 6800.
There's a reason it's easier to find the new AMD stuff in stock than nvidia stuff, they've got a terrible mining roi.
Vega 7 is a compute beast. The RX5xxx and RX6xxx are tuned for gaming performance and sacrifice unnecessary compute performance for better power efficiency.
No wonder the V7 is way better at mining.
And the reason you can't buy them is exactly the same reason nVidia is adding limitations - to try to make the cards less appealing to scalpers so the actual customers may get some.
Vendors and demand have effectively driven prices to an insane amount, and you just can't get them, unfortunately. Short of AMD doing something like Nvidia is doing here, I doubt we'll see them on store shelves any time soon.