I don't know enough to know why, but they were very interested in the extremes of size, both large and small, as well as the notion of infinite.

Fascination with the large seems to be a pan-cultural thing

https://en.wikipedia.org/wiki/History_of_large_numbers

The article does not talk about Mayan numbers, I would hazard a guess that they were interested in large numbers too.

There is also the Buddhist myth of Buddha enumerating a list of very large numbers.

https://en.wikipedia.org/wiki/Asa%E1%B9%83khyeya

https://jain108academy.com/buddha-recites-to-infinity-a-love...

Large numbers also show up in that problem posed by Archimedes.

https://en.wikipedia.org/wiki/Archimedes%27s_cattle_problem

https://sites.google.com/site/largenumbers/home/2-3/p12_2-3-...