Why Sicilian is common to play from grandmasters?

No, not because it is easy to play.

Sicilian is probably one of the most complicated responses to 1.e4.

The masters play it, because objectively it gives black the best chances to play for a win, but it is pretty theoretical and quite difficult to play properly actually.

Sicilian leads to unbalanced positions in which Black has good chances to play for a win. It is not easy at all (not that there are easy openings to begin with).

elo

No, Sicilian Defense is probably one of the most difficult and challenging openings to master. Its theory is massive and the positions are very sharp and risky for both sides. Most grandmasters play it because it offers a bigger chance for counterplay rather compared to other openings.