No clue, really. Maybe it's just me and my browsing preferences/patterns - but their stuff quite rarely shows up on uMatrix switchboard, and given that it has block-by-default policy I sort of visit its button quite frequently. On the contrary, I see Google domains a lot, like on every other resource (if not worse).

I really always thought it's monopoly - just Google. With some small or local vendors (e.g. Yandex ads are huge on Russian-language resources) here and there, but mostly just Google.