I can go along with the idea:
“Collecting is an instinctual behaviour and is genetically fixed.”
You can enumerate several reasons why someone collected:
-it gives respect and appreciation
-pleasure, sensory pleasure and aesthetic pleasure
-the excitement of the search for specific things and the hunt for more
-a combination of passion and pleasure
-greed, some collectors simply want more and more
-trade or investment funds, just for financial gain
-distinguish you, profiling, collecting art shows good taste
-attention and respect, image building prestige, ambition,
Add something to your collection works as a kind of antidepressant:
your body will reward you with a brief shot happiness.
Collection is also rewarded by a social component:
that of community life. (As in this forum).
A collector with a nice keris can make no impression on his neighbour, but he can during a keris-meeting. (Or the neighbour must also be a keris collector

)
But the question still remains: Why collect a keris ? And not an other form of artwork?
Why I bought as a child at a flea market among a thousand other things a keris? Or perhaps was it because the seller had a good story? And I also bought a story with emotion?
I have unfortunately no answer. I live in Europe and have no keris culture but I'm still interested in the keris, appreciate the craftsmanship, respect the culture. Therefore
I believe that it is a form of instinct.