The websites I mentioned use more cpu and memory than most games in Civilization the series, which are largely competently developed. My previous laptop could play civ 5 at a higher framerate than it could scroll github diffs or notion pages. Civ 5 handled full-speed keyboard input, while notion doesn't let me input text at my roughly 100 wpm typing speed.
I agree that we shouldn't be expecting users to figure out how to close the right tab, however I'm reporting the way things currently are, which is that webpages are poorly optimized messes.