Unfortunately, I think this is the case. Look at DuckDuckGo. It works for 90% of searches, but for that last 10% you really need Google. As a result, people use Google for all their searches.
I think this is another case of poor discover-ability. If you "discover" and understand how the bang syntax works, you can easily use DDG for your 90% of searches and only dispatch to Google when you need to. (e.g. "!gi dogs").
DuckDuckGo is great, but unlike Google which has immense brand momentum and recognition, it lacks the marketing to drive users to the service.
It's not perfect so people don't use it?
No, people don't use it because it has poor discover-ability and it isn't in other browsers, further reducing discover-ability.