As daft as it sounds there’s actually a valid reason Samsung uses Qualcomm in the USA and Exynos everywhere else and its down to patents.

Qualcomm owns all patents for building a CDMA modem and to access that large market in the USA it is cheaper for Samsung to use Qualcomms own processor than build an Exynos with the requisite modem in and pay Qualcomm royalties. (They actually agreed this in 1993!)

Because the rest of the world uses GSM almost exclusively Samsung don’t need the CDMA modem and so use their GSM Exynos which is both cheaper and royalty-free.

https://provscons.com/why-samsung-uses-qualcomm/

https://www.zdnet.com/article/qualcomm-blocked-samsung-from-selling-exynos-chips-kftc/