There are documents available for to mention that standard load balancer have monitor metrics: https://learn.microsoft.com/en-us/azure/load-balancer/load-balancer-monitor-log
But, I need to understand why do the basic ones not have any monitor metrics. Is it because of pricing? If yes, is there any official document to prove that?
No, Basic Load Balancers don’t support metrics. Azure Monitor multi-dimensional metrics are only available for Standard Load Balancer, which is also the recommended SKU by Microsoft.
Azure offers a Basic SKU and Standard SKU that have different functional, performance, security and health tracking capabilities. These differences are explained in the SKU Comparison article.
Upgrading to the Standard SKU is recommended for any production workloads to take advantage of the robust set of Load Balancer metrics.