- They might want privacy from Google. Using Google Pay probably doesn't make much sense.
- Security protection against Google. Google can remotely brick devices with unsandboxed Play Services. After blocking of ICC officials and all the Greenland threats, it's not odd that some European citizens would like to block this Google/US government attack vector.
- They want a clean phone without all kinds of crap like Gemini preinstalled.
- They want to reduce dependence on big tech/Google product in general.
In cases 2-4, using Google Pay with sandboxed Google Play services may be an acceptable compromise for convenience.