Haha because I'm crazy, basically.
Another option was 1717, but I decided for 1777
Probably like everyone is born on 17th day of a month, I think that the 17 is my lucky number.
I also think that ~1700 are a good number for a project like this: Pantheon is very expensive on my side, compared to my other limited editions (it cost the double of Dedalo Apeiron, for example) so print more than 1000 is helpful for me to recoup expenses. Do more than 1000 decks also increase the number of backers that can have it - I have an estimate of the backers who support me and would like to give the chance to have Pantheon to everyone (I hope I did a correct estimate!). On the other side, I wanted to do a limited edition to make it more precious, especially when the campaign will be over.
A trivia - technically, all Thirdway Industries decks are "limited", since I do a fixed number and I don't do reprints. The max number I produced so far is the Omnia Series and Dedalo (3000 decks per kind)