Why not? They are a competitor in the search space... Public, private, doesn't matter.
Well.. are they profitable?
According to the founder, they have been profitable since 2014.
Anecdotally, I've been seeing more and more success getting friends to switch over to DDG. This feels like early mass-adoption. It's rather exciting.
Well, except for chrome using their near monopoly on search to shove a browser in your face that further cements their place in search. and bundling it with the OS on mobile.
That's not a stable situation. The EU forced Microsoft / IE to unbundle - Google's day of reckoning approaches.