Why only in the US though? Wouldn't this be global then?
Quoting the news.
The Austin, Texas, company sold 495,570 vehicles from October through December, boosting deliveries to 1.79 million for the full year. That was 1.1% below 2023 sales of 1.81 million as overall demand for electric vehicles in the U.S. and elsewhere slowed.
There are many factors to consider.
For one, Chinese manufacturers still don't have full access to the "old continent", and I don't see any Rivian/Lucid here at all, so except some BYD, Porsche Taycan, KIA and the mentioned 500 and Mini plus the legacy Toyotas, there aren't as many alternatives here. The closest competitors currently are the BYD Seal and the Polestars.
Also luckily very few have the great idea of importing Hummers here, be the legacy ICE or electric.
So, hey, this is why the current model Y is still selling even after seeing the striking difference with the Highland. Simply there's no other decent alternative for SUV lovers.
But obviously this is changing. BMW and other incumbents are (slowly) catching up and their proposition is more suitable for the mass then Tesla, whose radical approach is more for early adopters like us (which by definition are a small fraction of the market, and the easy one to convince). And they even manage to piss us off as well, which is an accomplishment by itself.
This is why you see Tesla fixing some of the idiocy that went on until the Highland on the Y: it's the model most aimed at breaking the early adopters barrier. If it weren't for Mars, I wouldn't have been surprised if Model Y reintroduced USSs. Probably the next iteration will, once unsupervised FSD is mature enough to have mastered Vision only.
Last but not least: the best seller is the Model Y. The instant the news about Juniper went out, who would place an order until having certainty of the new model, and paying the old at full price, unless forced by circumstances? If Tesla had a traditional concessionaire model, you would see lots of deals to get rid of the last Ys, to avoid sales slowdowns. But afaik they don't.