Wellbeing is often reduced to a single number, income, life satisfaction score, or health rating, when in practice it is made up of several distinct dimensions that do not always move together: financial security, physical health, social connection, and a sense of purpose can each rise or fall somewhat independently of the others at any given time.
A country or a person can score well on one dimension, rising income, for instance, while another dimension quietly deteriorates, isolation increasing even as material comfort improves, which a single combined measure would tend to obscure rather than reveal clearly to anyone relying on it alone.
Reading wellbeing seriously means resisting the pull toward one tidy number and instead looking at several measures together, accepting a more complicated picture in exchange for one that reflects how a person or a population is actually faring across the range of things that genuinely matter to a decent life.