Well... Pagan culture got destroyed pretty heavily later. The traditions they were allowed to keep were just the first "fix", if you will. A christian would probably tell the story differently but from what I read it seems like they offered the pagans gifts to convert (like putting the christmas celebration pretty much at the winter solstice but also more material gifts). And once some of the pagans had converted (because to them it was basically just an additional promise of an afterlife for not much effort) christians got more and more upset that so many concerters didn't really take it serious and kept praying to their old gods in addition to the new one and consequently started destroying pagan places of worship (just see the story of Boniface chopping down the Donar oak for example) and getting more and more aggressive.
Also, I wouldn't really say the Europeans incorporated the new middle eastern religion into their culture - especially not in a cultural appropriation sort of way - because they didn't seek out this new religion, it was brought to them - and with increasing force. At first it might have been like "oh look, a new exciting story to tell each other around the fire", turning into a "have you heard? the neighbors are now going to that new church thing", then into "the clan south of here is now saying we should convert as well", to "we are now surrounded left and right by those christians and they're destroying our sacred sights", and in the end it was mostly "either we convert too or someone's gonna just take away what's ours". It's quite a depressing story if you read it from a pagan's perspective...