Same with Google's ads in general. For a long time they were whitelisted by default on just about every adblock list out there because they were so unobtrusive it didn't make sense to bother blocking them, especially when you compared them to the other ads that were common at the time. They were also generally relevant ads, so people actually did click on them and use them since it actually related to the thing they were searching for.
They're obviously more profitable now, but you have to wonder by how much and if they'd be a more trusted company today (and what's that worth monetarily) if they hadn't gone down this race to the bottom.
ETA: Part of what I mean is that now they create things like Stadia and most people didn't even bother trying it because they knew it'd hit the Google Graveyard in a few years. Had Google been a more trusted company, people may have been willing to give it a try and they could possibly have printed money since by all accounts the service was actually pretty good.