The biggest reasons I see is that Europe is still a collection nation states whit each having it's own language, culture, laws and needs, EU hasn't removed those (yet, god forbid). There really is no single market for many services like there is in the US, in Europe you have to develop and sometimes apply for permits and licenses for each country even with the EU, since EU usually regulates retroactively not so much proactively.
The second is that there is nothing like the US federal government or military that could fund and/or bootstrap tech companies with contracts. Like google, SpaceX and Microsoft have both benefited massively from taking lucrative contracts from military government and US intelligence agencies in the past. Those allowed them to grow and consolidate first cover the US and then springboard themselves global.
For like a two past decades at least this shit has not been about whether it gets limited to 1,5 degree limit, but damage mitigation. Just the systemic inertia made it unrealistic, because beside launching the nukes no solution was going to be snap of the fingers fast. If anything all or nothing alarmist has done more harm than good for the cause. Why give a shit if it's framed in the terms "we do everything now or all is lost, because feedback loops, but all the really really bad stuff will be like 50-100 years off in the future". Doesn't much matter if it was ever true, because it made shit propaganda, and the issue was always political, and a fight against inertia, not scientific strictly. The message should be damage mitigation, like what can be avoided if we do X.