The incumbent players are ignoring massive swaths of the addressable market at a time when, judging by my social media feed, there is renewed interest in labor issues.
A big reason for this is their reliance on a high-touch, manual onboarding process and slow, high overhead contract negotiation techniques. Prime for marketing automation, SaaS tools, chatbots, etc.
Additionally, for purely historical reasons, they have segmented the market by trade. There's no particular reason for you to follow this path, may as well help everyone get a better deal from their employer (and a cut for yourself!).