Groupon is a perfect example of a company that became irrelevant before reaching profitability. Most tech valuations are based on the assumption that the company's product will stay hot forever, giving enough time to cut expenses and turn black. While in reality, the crowd of early adopters that gave you the hockey stick growth, quickly moves on to something else once they get bored and then it turns out your market is orders of magnitude smaller than your investors expected.
I don't see a CDN as something that customers get bored of in the same way as coupons for random services.
When a consumer realizes they are getting 50% off of a service or product they didn't want or need in the first place, they stop signing up for deals. Also, once the businesses realize these customers don't provide repeat business and they are devaluing their product for consumers who do want it, they stop offering the discounts. Finally, it's trivial to sign up for each of their competitors and play them off of each other.
When does a Cloudflare customer stop needing secure, performant content delivery, and how easy is it to switch to a competitor?