aws loadbalancer,routeable confusion

I'm putting the instances behind the aws loadbalancer, I have configured the routable and attached the IGW to it, created the loadbalancer and added this instance to the aws loadbalancer every things work well, the endpoint URL of the AWS loadbalancer able to load the HTTP pages

Now i have removed the IGW from the route table and tested it again, the AWS loadbalalncer endpoint URL not able to load the page, but the instace status shows in AWS loadbalancer as inService

Why the IGW is required when loadbalancer is configured over private subnet, it technically Mean it's a public subnet, which is blocking me to create a NAT inatance