Every time I have to build a UI in canvas, I yearn for all the conveniences CSS and the DOM provide. Do people even realise how much trouble it is to make text wrap within a given space?
The UI of many games break if you scale the text though, if it offers such a feature (e.g. text won't fit in boxes). This is also the case on the web at times, but much less often.
And most games will use an engine like Unity or Unreal so they don't have to re-invent the wheel. HTML and CSS may not be perfect, but they've been battle tested for a good 30 years and have had improvements added. No need to re-invent that wheel.