AI-generated code still requires software engineers to build, test, debug, deploy, secure, monitor, be on-call, support, handle incidents, and so on. That's very expensive. It is much cheaper to pay a small monthly fee to a SaaS company.
No, they don't.
A domain expert armed with an Excel spreadsheet and the ability to write VBA macros will be enough for most business.
But the reasons the business software sector grew far beyond Excel of the 1990s is because of the inherent limitations in scaling solutions built by business analysts inside of Excel. There's a vague cutoff somewhere in the middle of the SMB market where software architecture starts to matter and the consequences for fuckup are higher than the cost of paying for professionally made software with, importantly, a vendor on the hook for making sure it doesn't fuck up.