I'm going to agree with @
CoogansBluff on this one.
Golf was the hardest to maintain a level of semi-proficiency.
Tennis takes a long time to develop skills to play decently.
Basketball/football/baseball all require teams and schedules, etc.
Competition is what sets some sports aside.
Many of us have not a single competitive bone-in-th-body.
Cycling is generally enjoyed without Winners and Losers.
I consider it much like Hiking = outdoors, fitness oriented, easily accessed, etc.
Swimming = much the same, but I never had access to a pool or warmish lake.
True, mountain biking requires special skills and better equipment can improve one's performance exponentially. But that's only one aspect of the sport.
Racing and fast group riding also = special skills only developed over time.
I ride with a neighbor occasionally. A fellow fit and thin, who never rode a bike as an adult. Over 2 years (no coach, not totally obsessed, etc) his endurance and enthusiasm are surprisingly strong.
JMHO