Aside from trying harder to reach those people, you possibly don't have a large enough sample. It is also possible you attracted the wrong people. For example, I'm in a space where there are lots of competing free products and we are a paid one. Just as one example, I had to put "free" as a broad negative keyword in AdWords to try to filter them out. Turns out there are entire classes of keywords that tends to resonate more with people looking for a free solution vs paid that I had to uncover and filter for.