The other thing is that the Kerala school mathematicians were somewhat isolated from any other potential schools of knowledge in Northern or Eastern India. There's no real evidence of communication with anyone outside of Kerala (aside from some fanciful theories about their ideas making it to France through Italy). Leibniz and Newton, 200 years later, were very much part of a broader European mathematical community.
Edit: Incidentally, does anyone know if the Kerala mathematicians knew of or read the work of Bhaskara II, who lived a couple hundred years before they got started? I assume so, but I can't find a source that says so.
Cheers,
Ganesha
It is a very reasonable supposition.
It is also possible that Bhāskara II's work made its way westwards via Arab traders and possibly Leonardo of Pisa (also known as Fibonacci, yes, that guy) may have heard of it (although no proof of that I'm aware of). He introduced the modus Indorum, better known as Arabic numerals to Europe and worked with the leading Arab mathematicians of his time (13th C.). He was definitely a part of the conceptual train that eventually gave birth to Calculus.