burning cards when all in

just wondering why dealers bother to burn cards when, say, 2 players are heads up and all in.
I know the reason about marked cards, but if 2 players are all in pre flop it doesn't matter whether they able to recognise the cards or not.
Is it just tradition, habit rules or what?

Its tradition they started burning cards because of cheaters a long time ago I believe.

its the rules which were bought about from people cheating with marked cards

True, the burn cards originated to stop/minimize cheating. However, the formal dealing rules for Hold'em don't change jsut because of # of players or who bet how much or who is in or out.

Dealing is done the same way every time. This keeps it fair to all in every respect.