Because I'm not the only one to offer these or similar services in the grand scheme of things nothing much would happen if I stopped working.
On a smaller scale, however, my clients might either end up with less efficient solutions to their problems or no solutions at all, which often means that plenty of manual work would be required to compensate for process shortcomings.
Hence, time and money would be wasted that might've been put to better use.
In terms of the coaching aspect of my work, developers might take longer to become proficient in their new framework / language of choice. They also might be able to produce value in a new framework but they might do so using best practices they know from an approach they used before, which is common when for example transitioning from C# to Java or formerly purely back-end-based work to work that involves web front-ends, too.
This in turn could lead to low software quality and ultimately unmaintainable software.