e-Tickets can be sent out instantly. They can't be lost or damaged. They can be re-sent if there was a communication error (e.g. a bad email address). They can't be counterfeited (while a PDF could be copied, for example, the bar code is only valid once). The cost to the team is the same for 100 tickets as it is for 100,000.

For those who like to collect their physical tickets for posterity, I fully expect that souvenir-type tickets will be made available for an extra charge :)