Because they used to produce dubious code leading to poor rendering result. I would like to say the Web was poorly designed but that would be too generous. The

Because they used to produce dubious code leading to poor rendering result. I would like to say the Web was poorly designed but that would be too generous. The Web wasn’t designed at all. It’s a hodgepodge of poorly thought out technologies hastily cobbled together. It’s a piece of technology designed to display static textual content horribly contorted to make applications. It took decades for JS and CSS to reach a state I consider barely useable and the best we could do is apparently flexbox.