The blockade are related to rocket bombings, not suicide bombings. The blockade's two main goals involve rocket bombings:
1 - Block the Hamas' access to weapons and weapon-making materials, or things such as construction materials which would help them in acquiring said weapons or weapon-making materials.
2 - Reducing the Hamas' influence over the Gaza Strip.
Obviously number 2 isn't working, but it doesn't matter. Number 1 is working, for example two Iranian ships have been caught during the blockade that tried to smuggle many tons of weapons, bombs, missiles, grenades, etc.
If the blockade wasn't imposed not only these two ships wouldn't have been stopped, but the fact that there is a blockade is a deterrence to anyone who'd like the Hamas to acquire weapons, without the blockade these two ships would have been nothing compared to the amount of ships that would help the Hamas.
The rocket attacks against Israel which are occurring on a daily basis and cause minimum casualties aren't the cause of the blockade, they only serve to legalize it. Without such rocket attacks Israel wouldn't be considered to be in an armed conflict against the Hamas, and thus a blockade wouldn't be legal against them.
The blockade's cause is not to stop the few rockets that are currently being fired on Israel and cause minimum casualties, the blockade's cause is to stop bigger, stronger rockets which can reach farther and would be fired more frequently, from reaching the hands of the Hamas and being used against Israel.