Each basic Mahjong Candy match is worth 100 points, and you will want to match your multiplier tiles as early as you can to maximize your Mahjong Candy score.
However, you can see that one of them has another tile on top of it, so it cannot be removed.
If you look at line 3, you can see that only one tile is free, the other tile is blocked by two other tiles and so it cannot be selected.