I get your point and yes, a basic sign-up or login flow can take a few hours to code using a framework. But when you start adding features like OTPs, social login with account linking, conditional logic, data validation, 3rd party widgets to verify identity or link bank accounts, automations to send a welcome email, store the data in your CRM, etc. And as you grow, more things come up and that's when this starts to get messy and most of the time you regret reinventing the wheel.