[PeterisP]

The timezones would have to be much, much more complex than now.

The noon-based timezones change on the east-to-west axis; and the difference between two locations is static; i.e., if my noon is one hour later than your noon, then it's always one hour later than your noon.

However, sunrise based timezones would depend also on the north-south axis, and shift during the year! If my sunrise is one hour later than your sunrise, then at a different month my sunrise might be at the same time as your sunrise, or two hours later than your sunrise (depending on our locations) - and cities moving between timezones every few months is a bit inconvenient.