Did they skip a strategy session as part of their process? 

It's not just about watching you work, although it's definitely important that they understand your business, industry, and competition. Content marketing (whether it's branding, social media, or regular content creation) should involve getting to know your vision, your personality, your voice. It takes patience and true interest in the client. I'm willing to bet the folks who failed you simply didn't try hard enough to find out who you are.