Can the license simply have a clause that user is not in Amazon, Microsoft or any public cloud provider?
Sure. It wouldn't be open source any longer, tho.
Is there a reason that a new style of licence that prevents the "fork and suffocate" approach of these large companies can't be ratified as fitting with core open source values?
Being dogmatic about the definition of open source, and not allowing that to evolve over time, feels like hard times ahead.