Startups generally have a bias towards doing things that they can measure accurately. This leads to heavy reliance on highly attributable channels like AdWords since you can target people who have expressed high purchase intent. What most companies don't do is look closely at multi-channel attribution models and look at how multiple exposures across different media types change purchase behavior. Perhaps someone who is exposed to two display ad driven messages prior to seeing your Google ad is 2x more likely to click and 4x more likely to purchase vs. just being exposed to your Google ad alone. I'm not saying that's what you will see, but you should be curious to understand those effects.
We tend to generalize based on our own experiences. I also don't think Facebook ads work well in many cases but I also can see brands that are doing a great job or run innovative campaigns that get their message across effectively so I know Facebook works if you get it right. Similarly, many folks give banner ads, mobile CPA ad networks, or TV a shot and see poor outcomes without knowing whether it was poor creative, bad media planning, loose targeting parameters that contributed to the poor outcomes.