There are many cases where the company might only use a fraction of the features (and therefore complexity) of the SaaS and so only need to develop and maintain those features they actually need. That's when ditching the SaaS can make sense if you can easily develop/maintain what you specifically need on your own with AI assistance.

Even if they use it less, if you combine all of the Saas products used by a company, thats a tiny fraction of the overall CapEx. And this cost is tax deductible, so there is no reason to optimise it unless Execs are really penny pinching, but at that point that company isn't worth selling to anyway.