Decades ago they relentlessly optimised that page, shaving it down smaller and smaller. Then suddenly they stopped caring, round about the time they gave people customised landing pages with extra junk littering the page. It must have made a palpable difference to their connectivity and serving costs when they did that. That we're back down to a "paltry" 1.9MB (from a quick test I just did) is remarkable.. and yet so much more than it used to be.