Why are there no career paths for Messaging or SharePoint administrator?

There aren't any certifications for these as Microsoft focuses on role-based not product exams. Microsoft clearly focuses certifications on what they see as new or revenue growth areas; these are well established products. It is shame as there is demand for these courses and companies have sprung to address this gap e.g. https://www.specialistcourseware.com/ and https://www.coursewarestore.com/