I think that is due to a variety of factors, most importantly a massively screwed comparison.
Not every software engineer in the U.S. works at FAANG or even in the bay area or other hotspots. If you'd exclude venture capital backed companies and limit the statistic only to companies with a sustainable business model that will stick around for longer than they can raise new capital, then your average will certainly be a lot lower (and it will still include extremely high salaries by FAANG companies). But venture capital brings me to the first key aspect.
Venture capital barely exists in the EU. There are some VC funds and there are some European startups that managed to raise a decent amount of money, but they don't reach anywhere near the valuations of even early stage US based startups. With more money being in the game, it's obvious that those companies will pay impressive salaries to attract the top talent available. The have the means to do it and having a company with many FAANG devs onboard is almost a guarantee for a successful next capital raising round.
The next thing is the difference in how software is approached. For most European companies software is a cost center, not a profit center. The biggest EU based companies have a few digital products at best, most of them only being complimentary to the products they actually sell and make money off. That is a stark contrast to the US (especially certain areas) where a strong focus on digital products exist. And if you don't make money off your digital products its obvious that you want to keep costs down.
Next I want to go back to my initial reference to the SV area. The reason why salaries are continuing to rise is the extremely high cost of living around those companies. Is a $10,000/month really that high if you have to spend 3,500€/mo on rent alone (I have absolutely no clue about rental prices in the U.S.)? There is no doubt, software engineers in the bay area are far from poor, but especially with salaries that are so far above what you'd find anywhere else, its important to consider the actual cost of living for the area where those kinds of salaries are actually paid. As soon as the cost of living decreases, the salary decreases as well, even within the U.S. And the discussion about FAANG companies wanting to cut salaries for people who are full on WFH just shows that the costs of living are an important reason for the high salaries. The costs of living also include things like education (incl. higher ed), childcare, elderly care, health insurance, etc. All of those things are largely taken care of by the government in most EU states, unlike in the US.
Another reason for lower salaries is the actual cost of having employees (this is limited to my experience in Germany; can differ from other EU countries). Here in Germany taxes, public health insurance and public pension premium is deducted from your salary. But the cost of the employment goes far beyond the salary since your employer also has to contribute roughly the same amount to public health insurance and pension as you have to from your salary. So take the salary of a employee, multiply it by 1.2 and you get the true cost of the employees salary (excluding benefits like vacation time, bonuses or the 13th salary). Additionally, most EU countries actually have employee protection. Not being at risk of loosing your job from one day to another is a pretty nice thing if you'd ask me, but it also reduces the employers flexibility.
To summarize: American software engineers probably really make more money, even if you'd adjust to all the factors I mentioned above. However, the difference is nowhere near as dramatic as the numbers mentioned by OP make it seem.