While Palestinian leaders, their European allies and the UN say that killing terrorist group leaders, the Israelis feel that, as long as the attacks continue, killing the leaders will cripple the ability to plan and execute attacks. Historically, this is true. Successful terrorist attacks, especially against Israeli security measures, require organization, technical skills and experienced leadership. Israel also considers the European nations hypocritical, as these same countries did whatever they could to counter terrorism in the 1970s and 80s.
Meanwhile, the Palestinian government is feuding with itself. The terrorist groups are more popular than the government, meaning the government cannot crack down on terrorists without sparking a civil war.