Because we'd have everyone goofing off in a cap ship. What a fun future that would be!
I go on in my little train, and a pirate in a Spyglass demands my cargo. That would be so very great.
This has been a Satires and Sarcasms Production!
On a serious note, one million is more than enough to start a temporary character. I think going overboard (a pun, since this is a game about ships, space or otherwise) with one billion would be detrimental to it all.