Samsung do put the Snapdragon soc into some phone's in Europe as we've seen in the Samsung fe 5g and fold 2 phone's so I'm not sure why they haven't with the Samsung s21 line up.
As said they do manufacturer the Exynos so it would make economic sense.
I imported my N20 Ultra Snapdragon version from Hong Kong via WondaMobile and they paid all import fee's. So it depends on who you choose to use.
I'm sure you'll love your Samsung Galaxy s21 Ultra 👍
Current Phone > Samsung Z Fold³ 5G.
I suspect its down to economics; they make the Exynos chipset, its probably cheaper for them to use it where they can. They may well be contractually obliged to use Snapdragon in some countries (or contractually obliged not to use Exynos).
I also suspect 95% Samsung phone users will not know what a chipset is, let alone care or know which one is in their phone.
My first Samsung phone was the S9Plus, I never researched what chipset it had; I needed to replace my Blackberry Priv and I knew someone who had an S9 and I liked it. I know people who choose their phone by OS first and colour second 🙄