Because 2-factor methods are not limited to phones or apps. You can use your pgp key which is likely what most of the darknet markets use.
Gotcha...thanks for the clarification. I'm just kind of getting started in terms of browsing deep web sites, etc. and TOR, so I'm coming across a few things I don't quite understand. Another thing I'd seen was people who had their personal pages on .onion domains....but were still using their full names, etc. I just don't understand why one would want a .onion site and *not* be anonymous.
Yes, I am using the 2 factor Authentication now, and it is really just the Google authenticator app which you download from the store.
And there you can have multiple websites or bitcoin wallets in there, So you will stay anonymous if you want.
I personally really like the 2 factor authentication, because I feel safer putting my Bitcoins in A wallet with 2 factor Authentication.