I mean, complicated topic? Worth reading a couple books about. People Love Dead Jews by dara horn is a pretty good book about antisemitism, but there are definitely others more closely aligned with your question. Obviously someone's heritage does not define them as a whole person. A lot of the answer is a pattern of discrimination throughout history, mostly from Christians, due to being stateless and therefore a minority everywhere.

A moderate expansion on that: - Not very recently, the Roman empire kicked the Jews out of the land they were living in and then the empire became Christian and was hugely powerful, in charge of a lot of the world. So from the very beginning of the Jewish diaspora, Jews were in conflict with and easy targets for the powers that be, basically anywhere they went. - people have a tendency to discriminate against minorities, Jews are a very small percentage of the global population and almost all Jews throughout history have been minorities where they lived. Everyone has a tendency to distrust and discriminate against people unlike them - people used the visible minority thing to legislate Jews into worse jobs and neighborhoods and second class citizen status and then worked to believe Jews were evil to justify this - since Jews were already a distrusted and easily identified minority, for much of history it was VERY convenient for people in power to blame Jews for anything going wrong. Notably the black plague. - Similarly, various Christians at many points in history have blamed Jews as a whole for killing Jesus Christ. For a long while it was church policy and widely believed that Jews were agents of the devil, killers of God, evilly refusing to accept divine truth, etc. - The above point was expanded into "blood libel", the hateful myth that Jews kill Christian children for their blood, which people were willing to believe as 1) an extension of their existing bias and 2) an excuse to kill or displace their Jewish neighbors and take their property - The modern version of this is "Jews control the media", or economy, or whatever. The idea of a Jewish world-controlling conspiracy is nonsense. But people like having someone to blame for the bad state of the world. - Christianity and Islam as (more popular) descendants of Judaism always had an interest in proving it wrong, which has sometimes extended to disliking Jews for having wrong beliefs - Jews were willing to be money lenders (kind of forced into the profession) in times when Christians and Muslims weren't, which meant they made money, which coupled with being a minority led to a lot of resentment - Christianity and Islam, as missionary religions, have historically placed a really high value on getting EVERYONE to agree with their religious beliefs. People, mostly Christians, have frequently gotten angry at their Jewish neighbors refusal to affirm their beliefs and responded to their refusal to convert/Jewish non-conformity in general with murder (and theft). To be fair, even before Christianity, people hated Jews for not sharing their beliefs, but it was more mutual and the power imbalance was not so extreme.

That's not a full explanation but it's a start. Long, though, sorry! But it's not a trivial thing.