I don't think the big companies not making Sota models being an indicator that open source failed. If all semiconductor patents expired tomorrow it would still be prohibitively difficult to manufacture your own CPU at home or at work.
Me neither. But open weights are not open source in the first place.
It wouldn't be surprising that the raw intelligence of an LLM model has little to do with the architecture (which is the part most published).
The secret sauce, like how/what data gets curated and cleaned, has rarely been talked about. So, even if the labs upload their weights, competitors are very difficult, if not impossible, to replicate the technology independently.