Why Gigabit Ethernet Direct Connect is not default at Macs?
Gigabit Ethernet is new technology in wired networking so if you're using a crossover cable, it will only work up to 100Mbps. Use a straight cable instead.

In Wikipedia:


  An Ethernet crossover cable is a type of Ethernet cable used to
  connect computing devices together directly. It is most often used to
  connect two devices of the same type: e.g. two computers (via network
  interface controller) or two switches to each other. By contrast,
  patch cables or straight through cables are used to connect devices of
  different types, such as a computer to a network switch or hub.
  
  Many devices today support Auto MDI-X capability, wherein a patch
  cable can be used in place of a crossover cable, or vice versa, and
  the receive and transmit signals are reconfigured automatically to
  yield the expected result.


To make things easier to understand, network interface cards (NICs) back then were "dumb" so they still need separate lines for receive and transmit signals. Now, NICs can identify both in one line.