Apple and Samsung are (primarily) hardware companies, whereas Google is an advertiser. If your income depends on hardware sales, longevity/reliability is an important factor for your long-term brand reputation that you can’t afford to sacrifice.

Google-branded phones are essentially just another avenue for them to push Google Play Services, one where they can guarantee the platform experience they envision developing vanilla Android. I think they also serve as reference hardware, but the custom tensor chip on the most recent pixels sorta eschews that… unless they are pushing the idea of putting a TPU on Android phones.

Its similar to why NVIDIA(designer/manufacturer) doesn’t offer as good customer service or warranty on their graphics cards as EVGA (hardware/packager) does.

This isn't a super convincing argument cuz you can spin it the exact opposite way here(hardware manufacturers want to sell more devices, google wants people to be using their services and have as many devices in the wild as possible).

Probably here there's not a great overarching narrative of reasons, but I ... believe Apple controls more of the components in its phones and can do the management itself

Apple uses their own chips in their phones. Samsung also has their own silicon, though they do use Qualcomm chips in some models too.