Well, for games using Denuvo (and similar online-DRM) singleplayer campaigns are also an online feature.
For a proper implementation of achievements look at Shovel Knight (they call it internally Feats btw.).
A bazillion games have them, anything ranging from THPS to GTA: San Andreas to Primordia.
I would be surprised if Telltale’s latest Walking Dead game didn’t have them anymore. The “you made Clementine become the next big evil dictator” or whatever so-called achievement is fully offline. The optional online part consists of comparing your choices/achievements with those of others.
Steam is an online “feature.”
I think “we” don’t literally mean just any achievements.
Taking a look at my achievements for Gorogoa, for instance:
You can see I only have the dev tracking achievements without having any of the achievements that gamers presumably “care” about.
In Tomb Raider the achievements are slightly more meaningful (like those in GTA: San Andreas):
Rise of the Tomb Raider by contrast has added a whole slew of meaningless progression tracking achievements:
