I think the main point was that any price barrier over 0 dollars limits your audience, regardless of profitability. That literal pay wall simply makes people start to question. Especially if a "free" alternative exists and they don't care about the pitch (in this case, privacy or less low quality results in search).

That's arguably a good thing since a premium model mitigates the temptation of ad or data selling based approaches. But the fact is many don't care nor mind those as long as they aren't extremely intrusive. Even if they are (full page banner ad with small x), they may tolerate it anyway.