Why dont more standalone DACs come with ethernet???

The iFi is not a standalone DAC, it is also a streamer, hence the Ethernet.

The Bricasti M3 has an Ethernet renderer option that is very good. I have thought the same thing and theorized that it will slowly ‘replace’ (well, you know, maybe just in addition to) USB over the next 5 years. Ethernet doesn’t have the same level of noise issues USB can have, so why not?

DACs don't do ethernet.
Streamers do ethernet.
Ethethet and USB bi communication a 2 different things

There are definitely getting to be more available. Bel Canto e1X and Black EX DACs both have Ethernet input. Disclosure: we're a Canadian Bel Canto dealer.

Gold Note is another and there are more as well. But, still not very common at all.