Some companies have change ownership but that still doesn’t change the emotional memories. Then again you have companies such as IBM who developed tracking systems to gather Jews and systemize the Holocaust operation and have not apologized till this day.
And when you say who cares what companies did 70 years ago, just think about the next time you spend so much money to wear a suit in which the founder designed uniforms for Nazis to murder your grandparents in.
So yes certain things are more personal than others. Of course you can’t boycott everything the list would be endless including chase bank and companies that noone even knew had a big connection to the Holocaust. But you probably should and can easily avoid the companies with direct correlation to the Nazis.
Regarding visiting aushwitz I’ve read stories of how guards harass and mock Jewish visitors there or even say anti semitic things to them. The hatred is certainly still there. While it can be an important place to see, I’m not sure if it’s necessary. But on the other hand I feel that if people would stop visiting the place would not be kept around and possibly destroyed or just wasted away. And it’s a living proof of history so not sure what the right thing is for that.