A 2 person startup cannot provide a dedicated developer for your account, a personal contact for each of their thousand customers, is at high risk of being acquired/changing their business model/founders abandoning it, etc. For enterprise, long-term stability and personal contact matters more than price. A typical SaaS contract is 0.x% of yearly revenue of big corps and nobody wants to be the one person risking the business for such miniscule savings. Another often overlooked part: Employees are the biggest cost center, much larger than any contract. So retraining a single team of 10 employees can often be more expensive and more disruptive to the business than just sticking with a legacy provider and established processes.