You're right that for most, there isn't a business case to care about access to these sanctioned countries (there are more than just those two that Google is blocking). I wouldn't say you won't be locking out any users: people in Iran obviously do use, say, source control. But sure, the monetary loss is very limited.

But ideology can be a powerful reason. And people in Open Source can be very ideological. Certainly for me, this makes Gitlab a no-go. I want my code to be accessible by everyone. I do wonder what kind of pressure could be applied to Gitlab in terms of free software developers shunning the platform.