That's likely to be an implementation detail of how they've implemented TCP routing across a large fabric.

AWS doesn't decide or even care about this, customers configure security group rules for their own services. Nothing is allowed by default, so if you want ICMP you would need to allow it, most font bother because it's not that helpful in a cloud environment (can just monitor the TCP port instead and get similar information).

This explains why some people have problems with IPv6 - if you block IPv6 Control Messages, then it will only work sometimes.

Fragmented packets won't work without ICMP.

Edit: here's a good page about the effects of disabling ICMP: https://www.rimscout.com/why-you-should-not-block-icmp/

Also there's some blackhole detection or how is it called.

However it's OK to block _parts_ of the ICMP protocol for security reasons, like echo and reply.