Because you can always outcompete them?
No, it is not a first class ticket to unicorn valuation, but it is trivially easy to differentiate
- from Google by just providing any kind of customer service to all paying customers
- from AWS and GCP just by allowing on premise solutions
- from Facebook by not reliably failing to protect and/or actively exploit your customers all the time
- etc
Need proof? See Slack, WhatsApp and Instagram (before the acquisition), Basecamp etc etc.