Historically, FMA was not taught in public gyms or open commercial spaces; it was passed down through tight family lines or via highly selective, private mentorship. Masters were notoriously protective of their "counters to the counters."
Furthermore, The most devastating of these occurred during World War II. During the Japanese occupation of the Philippines, many of the country's fiercest practitioners used their blade and stick skills in active guerrilla warfare.
A massive number of top-tier masters were killed in action during the war. When they died, their specific family systems and highly refined combat experiences died with them.
As FMA spread globally in the late 20th century, it underwent a massive transformation to fit into Western business models and international sporting formats (like tournament Arnis with body armor and padded sticks). While this saved the arts from total obscurity, it altered what was being taught.