The primary answer is buried in the article, in passing: "And when even 10% of Los Angeles’ population got behind the wheel, their presence so slowed the streetcars, which lacked their own lanes, that they could no longer make their schedules, and their level of service declined overall."

European streetcars typically have separated lanes and loading areas and thus don't mix with automobile traffic. That way they aren't in conflict. When roads had largely low speed and uncontrolled use, streetcars worked fine because people were used to and able to stay out of each others' way. The automobile was dramatically faster and more dangerous, and the laws and infrastructure were gradually adapted to it (e.g. traffic signals, left hand turn rules etc).

Streetcars in the US, and I suspect in other places where they have failed, had to intermix with automobiles, which lead them into a deadly spiral.

The other factors mentioned in the article (reluctance to spend, reluctance to run a centralized system, regulation, etc etc) applied in Europe too -- we have a survivorship bias when we see the streetcars in Europe. Look at Berlin as a great A/B experiment: in the west the streetcars were torn up while in the east they were retained. I much prefer living in the east (today!! not under communism) because the Straßenbahn is so convenient. My kid took it to school.

Some streetcars survive or have been revived in the US -- it's called "light rail" because I suppose "streetcar" is a laden word. They pretty much all have dedicated right of ways, and if not (I'm thinking of parts of San Francisco's MUNI) they have dedicated loading areas and exclusion zones -- except for cable cars :-)