Why can't the server get the client MAC address, like the client IP?

Question

From what I know, all the MAC addresses that the packet gone through are in the packet. This is because that each packet that goes in a certain path, should also be returned

Answer 1

Actually, the MAC-address stored in the packet is changed on every hop of a packet's journey.

MAC is shorthand for Media Access Control, with media refering to the local communication media. While source and destination IP-Addresses remain the same throughout the journey (and are used for long-distance routing decisions), the source and destination MAC-Addresses just indicate the next hop.

Because of this, the MAC-Address stored in packets received by your server should be the MAC address of your point of presence-router, or of the equipment of your provider.

You might want to have a look at the OSI Layer model and encapsulation.