Why do you think that many people didnt notice the harassment of German Jews?

People did notice the segregation and marginalising of the Jews. But much of the harsher treatment of the Jews was kept hidden from the general public. Those who lived near the railway lines or near the camps certainly did notice the treatment, but again, did not know the level or the extremes of the treatment.

Also people wanted to remain oblivious; there were enough bad things happening in the war, everyone was suffering, people themselves could be at risk if the asked too many questions, it was safer to ignore what was going on and rationalise it away.