The low sample size makes it untrustworthy for drawing conclusions about subjective user preferences

Usability testing is often confused with market research, but the two are very different.

Usability problems can easily be detected from a sample of about five test participants. Very different kinds of people will tend to encounter the same usability problems. More than seven participants is just a waste of time.

Market research issues, things like design-preferences and whether they would actually want to use the product, are completely different. These vary wildly from person-to-person and different personalities/backgrounds. You need big sample sizes to judge them accurately.