Analyzing the קִיְּמוּ וְקִבְּלוּ episode. If it is actually a valid complaint, why were the Jews punished for sins in the Biblical Era?

Was the mountain held over their heads at Sinai to compel them to accept ALL the mitzvot? Did the Jews not want to accept ANY mitzvot? Or just some of them? In other words, what actually happened as a result of Purim?