My guess is that a lot of users aren't careful with their post-mixing behaviour (many mistakes can be committed here, often unwittingly).
Most likely, i've seen users who ignore anonymity color (green, yellow or red) or use all inputs at once.
Good point. The only alternative is only buy digital coupon or gift card if you want to buy something from specific store.
BISQ.
Or create good/trusting relationships with trustworthy traders in LocalBitcoins, then trade directly. Because the true potential of Bitcoin might only be attained through peer to peer trade/commerce, and the incapability of a centralized third party to censor you.