That's because Dak is turning them down. HE turned down last year.
Prescott did not "turn down" the Pro Bowl - last year - or any other year.
He was selected twice - for his 2016 rookie season, when he was one of the two reserves (behind the starter), then following his third year in 2018 as an alternate, when the selected starting QB Drew Brees opted out of participating due to injury.
Perhaps you're getting confused about a player receiving Pro Bowl honors - but not participating in events days before the game and the game itself.
Every year a number of players selected to the Pro Bowl don't go to the event. The two main reasons are:
1) The player with his team just participated in the Super Bowl;
2) The player declined because of injury(ies) that occurred toward the end of the season.
That is why Pro Bowl Alternates are voted on (by players only) after the official Pro Bowl teams for each conference have been announced -- these alternates will go to the event in place of the players who opted out (usually for the two reasons stated above).
Players that are selected to be on the Pro Bowl team are still Pro Bowl "honored" even though they do not go to the festivities and game.