And almost all of them gave up developing their own engine except Apple and Mozilla?
FYI, WebKit itself takes hundred of engineers from Apple (which would be roughly similar to Blink). And this is only for the rendering engine, which is pretty small compared to the entire browser codebase. Thus Apple is investing a comparable amount of engineering resource into Safari. Where are "Other browsers"?
Please don't assert this so lightly unless you have any evidence to support it. A rendering engine is just a tiny fraction and you gotta take care of literally thousands of other components to build a modern browser. This applies to Chrome, Firefox and even old good IE. I don't expect any valid reasons why the same logic cannot apply to Safari.
The number above is probably pretty close, but there's a misconception that WebKit is only a tiny fraction of Safari: it's not. Most of the manpower and work goes into it; Safari is just chrome around it (albeit chrome that does take a reasonable amount of work to make…just not as much as it does to support JavaScript and WebAssembly VMs, page styling, rendering, WebGL and WebGPU, networking, tracking prevention, and maintaining support for the the ever-growing list of web standards WebKit supports and participating in discussions on shaping them). Safari is just one of the clients of WebKit.
FYI, WebKit itself takes hundred of engineers from Apple (which would be roughly similar to Blink). And this is only for the rendering engine, which is pretty small compared to the entire browser codebase. Thus Apple is investing a comparable amount of engineering resource into Safari. Where are "Other browsers"?