Also we should remember the first worm was targeted at UNIX systems.
We should also remember that the 2nd worm was targeted at VMS systems (https://en.wikipedia.org/wiki/Father_Christmas_%28computer_w...) and appeared only a month or so after the RTM worm. Imitation is the sincerest form of flattery, no?
Also we should remember the first worm was targeted at UNIX systems.