Attacking an international event on German soil and killing Germans as collateral also is pretty much attack on Germany, no country with some self respect let's others attack openly in its borders.
That wasn't the only Palestinian attack on Germany, they also hijacked Lufthansa planes.
What 1972 has to do with Gaza today? It's at least a quarter century later than the WW2 guilt you brought up.....
If you really want to understand why Germany built it's relationship with Israel post 1972 and started hating Palestinians, it's because they did the same thing that hitler did, kill Jews on German soil, Germans tried to hold their first Olympics after hitler held the last one in Germany, Palestinians trashed all that effort and image with one terror attack.