Maybe there is a reason why the Buddha appears in a warm-climate country (Jambudipa = India) rather than somewhere in Siberia for example. But that does not mean that Buddhism cannot spread to other geographical areas. As we can see on the Vinaya stories, when monks went to live further away from the Ganges valley, they asked for special permissions regarding clothing, shoes, etc. and the Buddha made such allowances for them.
Kiṃkusalagavesī anuttaraṃ santivarapadaṃ pariyesamāno... (MN 26)
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