- Because it is too big.
- Because it is more expensive
- Magnets are not without problems. I often carry my phone next to my credit card and the magnets in the mag-safe port are strong enough to erase the magnetic strip.
- A phone (or ipod nano !) is much lighter than a laptop. The benefit of having a connector that snaps off when pulled accidentally is greatly reduced. Either the connector will be too weak to hold well in normal situations or it wont prevent the device from falling.
They just need to support the connector properly and it won't break. Because it contains no moving parts, the micro-usb connector can be made pretty sturdy.