I once heard it said that words that existed longer ago often ended up the same in modern languages which are of the same family, for example, hand, hand, and hand, in English, Swedish, and German (resp.).
There may be some flaws in this assumption. One is that there is nothing stopping the word from changing or being replaced by a different one, in one of the languages. Sort of like, we used to welkin, but now we say cloud.
It is also common for the same word to spread laterally (across unrelated languages) extensively, like the word iPhone in so many languages today.
In spite of all this, I find it surprising how many different words for cream there are in Germanic languages.
And perhaps there are more examples. (“Als Rahm bzw. im bundesdeutschen Hochdeutsch auch Sahne, im österreichischen Hochdeutsch auch Obers und im Schweizer Hochdeutsch auch Nidel”, Rahm)
I did look at the list of translations of the article and I did see a number of recurrences of cognates across other languages, so maybe it really isn’t so mysterious. Crema appears to be of Latinate origin, which has spread to some non-Romance languages - English by way of the Roman Empire or France, presumably. The most fundamental word coming from old Germanic origin appears to be “Rahm”, which features in Icelandic, Dutch, and some other languages. I do not know if grädde actually drifted from the word “cream” (c -> g), but I find it unlikely since I see no reason the form would change so much in such a short time frame.
So, even if the origin of each word can be explained, it doesn’t satisfy the broader question, which is this. There is probably a kind of “inertia” in languages where it is natural for people to keep using the word they have. It’s an emergent phenomenon given that in a group of people all using and reinforcing the same word, there has to be some particular reason, some force of energy against the default norm, to start using a different one - “an object at rest remains at rest until acted on by an external force”.
So if “hand” has remained unchanged for so long, why did cream get so much leeway to vary, amongst languages? I think to make sure you understand the question, in case you were to say, “Because the Romans came along and brought their word ‘cream’ with them” - sure, but why did the old Germanic word “hand” stay so fixed even in the presence of alternatives, whereas “Rahm” did not? Is it a coincidence, happenstance, or can we note correlations where some words have more of a proclivity to being newly adopted than others, based on their meaning? It sounds unlikely, honestly. My guess is actually that it’s just a huge coincidence. Sometimes anomalies occur and people seek explanations, whereas the answer is it just so happened that the word for cream happened to shift around a lot in neighboring countries, while the word for hand did not. It may have just been arbitrary and accidental, the unpredictable unfolding of world phenomena.