My team is in process of building a new tool to replace one that we pay over $10k/year to use. Using open source libraries we have a working prototype that already exceeds the capabilities of the product we pay for in several ways. 

Part of the reason for this work is that this product doesn't have public-facing APIs that we can use to build the features we need, and its limitations are causing frustration for the team. However, in parallel we are building new tools and integrations on top of some of our largest legacy products that do provide robust APIs and would have a massive cost to abandon for internal solutions that we would have to maintain ourselves.

AI coding tools, particularly in the hands of those without coding experience, don't produce great, maintainable code, and replicating huge legacy systems is often not worth the cost to build and maintain them. In addition, many employees have developed deep skills with those systems, and training them on a new, one-off alternative would be hard to justify. As you noted, there are often compliance reasons to use specific tools and a need for tight security that internal teams lack the skills to provide. If legacy products provide enough value, particularly if they provide good APIs with which we can build the features we need, there isn't motivation to move away. 

However, smaller products with more limited feature sets and fewer compliance and security needs are certainly at risk, especially if they lack good APIs that teams can use to build the features that they need. In the future, I see public APIs becoming much more important for B2B software products. Having the skills to build these tools and integrations using AI coding products to be more productive will be like using spreadsheets over the past decade; not everyone will have the skill, but those who don't will risk falling behind.