It is happening though internally in businesses I've worked with. A few of them are starting to replace SaaS tools with custom built internal tooling. I suspect this pattern is happening everywhere to a varying level.

Often these SaaS tools are expensive, aren't actually that complicated (or if they are complicated, the bit they need isn't) and have limitations.

For example, a company I know recently got told their v1 API they relied on on some back office SaaS tool was being deprecated. V2 of the API didn't have the same features.

Result = dev spends a week or two rebuilding that tool. It's shipped and in production now. It would have taken similar amount of time to work around the API deprecation.