The dullness comes from their approach to possession. Ball movement, pinball buffer players. The passing, stroking it around. Very little on the ball movement. Conservation of energy. It was effective in the same way slowly removing oxygen from a room is effective at killing people; you'll be asleep before it matters.
Their winning run in the 2010 World Cup was lamentable:
In the group stages they lost to Switzerland, beat the mighty Honduras 2-0 and ten man Chile by one goal.
After that it was a drab procession of four wins with just four goals scored. Dominant possession, very little dribbling, yawn football. It's my least favourite World Cup winning team of all time.
They were more lively in the 2012 Euros but still sterile. Italy got a thumping in the final but one swallow doesn't make a summer.
The Dutch smashing them 5-1 in 2014 was a catharsis for world football. A death to the tyranny of dull. I was so pleased to see them get beat like that; and so die all traitors! And so forth.