There's also considerable risk-aversion at large enterprises. Getting themselves into a position of significant dependence on a SaaS provider can be unappealing for at least two reasons, even if the pricing works for them initially: 1. risk that the pricing gets raised significantly, or the business's employee/customer profile changes in a way that raises the price to them significantly; or 2. risk that the SaaS provider goes out of business, is acquired, pivots, or otherwise significantly changes the service.
Building something in-house probably doesn't usually result in a better product up front (and definitely not for less up-front expenditure), but it can reduce some risks and be less constraining to future moves if you own the app.
