If something is global, then it does not spread like a thing that is local. Why
fresh air does not spread like polluted air? Why fresh water does not spread
like polluted water? Over time, there have been different divine entities who
have illuminated the reality relevant for that specific time and space. A child
when illuminated about something new that s/he finds relevant becomes an
impassioned devotee and begins spreading that left, right, and center as if
that is the only truth. Consequently, anything new spreads like wildfire and
eventually ends quickly, just like Buddhism ended quickly in India when Adi
Shankracharya fed the dose that the Buddhist leaders were giving to convert
Kashmiri Pandits into Buddhist monks and appropriate Kashmir Shaivism
knowledge base as the Buddhism knowledge base. That dose was to do a
debate and defeat the opponent, and convert all the followers of that opponent
along with that opponent to your belief system.