Unfortunately Google would make the Gmail team very grumpy if they did this - Gmail's by far the worst offender in my experience. Every single time I open my email I have to remind myself to wait for a moment before clicking on my newest emails, because most of the time there's going to be a couple ad "emails" popping in and shuffling everything else down a few seconds after all the real emails have loaded.

Google's grumpiness is an excellent measure for how much we need a feature. The grumpier, the better. Other browsers should do it. Firefox, Safari, Brave, everyone else.

Maybe something that Firefox and Safari could implement then? :)