Why only 13 root servers are available in the world?

Could you please elaborate on why there are only 13 root servers available globally? Isn't this a limitation considering the vastness of the internet and the increasing demand for domain name resolution? Is there a specific reason behind this number, or is it merely a historical artifact? Moreover, how do these servers manage to handle the massive load of DNS queries from all over the world without experiencing downtime or latency issues? I'm genuinely curious about the underlying mechanisms and rationale behind this seemingly arbitrary number.