Hasn't Servo been around much longer than Ladybird? Has it stagnated?
I believe the article makes clear that they have.
>Servo main dependencies (SpiderMonkey, Stylo and WebRender) have been upgraded
There’s simply more C++ programmers around, and you need as many bodies as possible for such a large project. There’s also precious few Rust developers with experience with large projects since Servo is the largest project.