I did load test on AWS S3. Results are confusing

I did a load testing on a static file hosted in S3. Performed 50K GET requests per second, over a minute.

When I used the http URL, it worked fine. 100% requests got HTTP OK status, and the avg response time was 15ms.

When I tried https URL, it couldn't go beyond 20K req/second, after which the requests are getting timed out.

What could be the reason? Does anyone know how many req/second can a static file hosted on S3 handle?