Props to him for that almost decade of time investment. My attention span and lack of patience would have perpetually disqualified from maintainer on any linux distribution. The trade-off never seemed to be worth the effort either.
Is there further evidence you have that specifically relates to the specific decision of this particular dev to step down from Arch?
As you yourself say, being a maintainer is a big commitment, one that many people naturally tire of as their interests, goals and other life needs change over time.