Optimized games have a well known impact on sales. I'd assume the same with trading software. Putting out a blanket statement that web devs are lazy is just silly. Developers rarely have much say in how much time they can dedicate to features and the app as a whole, that usually boils down to PMs and management. If the org as a whole doesn't value performance or doesn't think it matters, then that will get reflected in the product regardless of what the developers actually want.