Availability.

Platforms with no country requirement: you can start these from wherever you are, get paid internationally, and take them with you if you move. This is the list to work from if the local options where you live are thin.

Platforms that only work inside one market: the local ride-hailing app, the national classifieds site, the regulated broker that needs a resident tax ID. Useful precisely because they have less competition than the global platforms, as long as you're in the right country.