Maybe just the market fragmentation. For example, a lot of the robocalls in the US are trying to sell extended warranties for vehicles, student loan debt services, health/life insurance, scammy tech support, etc.

If you target the US, your sales pitch can be in one language, with roughly one set of commission paying providers, and super cheap VoIP calls. I assume that would be harder in Europe due to language, state provided services for health+education, more strict laws on loans and warranties, differing costs for local VoIP numbers, etc. You would likely have to tailor for each country.