Why are vertical moves often considered the most easily quantifiable measure of career success?
Answer
Because the corresponding title change and shift in the reporting structure are clearly defined.
Vertical progression is easily measured because moving into a role with greater authority results in clear, documented shifts in job title and reporting lines.

Related Questions
What describes the inherent structure of the traditional career ladder model?What action directly corresponds to climbing the traditional career ladder?What is typically the primary motivation for executing a lateral move?How should a lateral move be strategically framed to stakeholders to be viewed positively?How does the career lattice structure differ from the rigid career ladder?What distinguishes career development from career growth?What is characteristic of the hybrid organizational approach to progression?What purpose do defined career tracks serve within an organization?What can career advancement encompass besides a higher title or salary?Why are vertical moves often considered the most easily quantifiable measure of career success?