Not going to pretend to be able to read the minds of Hamas. But it seems like the idea was that taking hostages would give them leverage to negotiate. Because although the Israeli government generally regard Palestinians as subhuman barbarians, surely they wouldn't risk the lives of the hostages by retaliating full force. And it seems in general they were partially right. The general population of Israel is calling for a ceasefire because they are concerned for the safety of the hostages and want their friends and family back. But Netanyahu seems to have very little interest in negotiations.