I would venture this: They are told to do so by the TV presenters. It just makes for better TV. As a TV presenter (and as a viewer) you would like to watch each player as they look at their cards. Why not enforce it as a rule?
Example of rules:
The current rules for TV broadcasting for the 2013 European Poker Tour include paragraph 41:
During all broadcasts you acknowledge and agree that, if so requested by PSLive or an affiliate (if the Tournament is organised and operated by such affiliate), all players must remain within pre-designated locations whilst on all breaks in play throughout the duration of the TV Table, and that in such event, the players will not be allowed to leave these locations, at any point, without being accompanied by an appointed tournament representative. You further acknowledge and agree that players might be required to show their hole cards to the hole card cameras on the TV Table on each hand they are dealt, unless the player has declared that they are playing the hand ‘blind’. PSLive, or the affiliate, shall have the right to halt play, within reason, on the TV Table until all hole cards are displayed by all players in play.
The second half of the paragraph is the most relevant and if you take a look at that last sentence, shall have the right to halt play to have time to show all the hands. This means that the TV presenters can (and probably do) enforce players to look at their cards in order.
This answers the main question, why they wait for each other, but not why it possibly could be advantageous to wait even if you are not forced to.