Some people, (eg people who aren't already Brex customers), aren't going to get that email, and aren't following Brex's social media presence. They may not even have a social media account of their own, not even a Linkedin. The only way they would hear about is is via their landing page.

How much you use social media, and are a Brex customer, is going to influence how big you think that group of people is, but it's for sure, non-zero.