Two reasons:
- It's a connector thing. Too many different connectors out there. Blame the manufacturers.
- The technology changes so fast that it is impractical to try and cover every possibility.
- Travel chargers for most phones are small and light. If you're lucky you can charge your phone through the usb port on your computer ala Blackberry or most all the PDA phones. If that's the case then check out the retractable cables by Zip Linq .
Ok it was really three reasons.