http://poolpicker.eu/text.phpMiddlecoin 0.00573754
CleverMining 0.010628
WafflePool 0.00940643
HashCows 0.015
everybody here could be paid 3 times more than middlecoin by using other pools,
anyone can explain why waste mining power to the least profitable pool?
Except the top pool in your list, HashCows, has been the worst pool on average the for the last month. It's good to see them doing better but they wouldn't have been a very good choice most days -- even worse than MC.
Every pool in that list has been on top one day in the last five days. You never know which one it will be. That's your answer.
incorrect. from poolpicker.eu:

middlecoin hasn't actually been on top for the past 5 days; middlecoin actually is the lowest-per-mh for 1day, 3day, 7day, and 14day averages.
poolpicker also indicates for 1day and 3day averages hashcows is currently better, and clevermining has the highest 7day, 14day, and 21day averages.
while the scatterplot line chart shows peaks for middlecoin, the daily averages tell a different story because it corrects for the large 'unexchanged' dumps middlecoin likes to do every few days.
while we don't know which pool is going to do better on any given day, if someone doesn't want to micromanage pool selection the broad trend is middlecoin doesn't pay out like it used to.