Why is it that an ICMP packet does not have source and destination port numbers (wireshark protocol analyzing) ?

ICMP doesn't use a port, it's simply an echo - reply protocol NOT a communication protocol.

I made a google search and found:

ICMP is on network layer, where port numbers will not be added to the packets. Port numbers are added at TCP layer.

as a more technical description, that will do.

Layer 3 (Network) is responsible for "path determination" (lowest "cost" route) and "addressing" (IPs) so all it need is to fire out a signal to the remote node and get a reply back.

Here is a list of the ICMP parameters along with their respective RFCs if you want to get into serious reading material.