But they stopped reading it for showing contextual ads.
They're still reading it to show you useful information across Google properties, like in Google Maps the location of the theater you bought tickets to see a play to tonight. Removing that would be removing a useful features that people liked (unlike the ads).
I've had e-mail messages open in the GMail web interface that when I search for the words I can actually see on my screen come up with nothing.
I downed you before but can't undo it now it seems. My apologies.
There's no way to know if the email you were sent is spam without looking at it, in some sense.
But we learned over time that they're doing massive data trawling, in this case every purchase made. And as always there's a theoretical advantage...maybe in the future Google will identify when you can get something for less, etc. But the reward (much like the location of a theatre) is so tiny and abstract that if people had the choice most would say no thanks. Just as I don't need Google to tell me about my flights, I have much better alternatives for that. In each case the advantage is 99% for Google, 1% for the consumer, but it's coached in a "your advantage" pitch much like a Payday Loan company commercial that talks about how much they just want to help people out.
Google Maps on iOS a while back was seemingly irritated that I had its permission set to only see location while I have the app open. "But if you allow background logging we can tell you where you parked!" it whined. In return for giving Google the wholesale access to my location I would get this minuscule possible advantage. No thanks.
Or did "reading" in your post mean that you think people actually read and manually type in those lists?
Misleading suggestions, as they had stopped parsing them to attempt to generate adverts from the data they could gather there, but continued parsing for other purposes.
Just recently someone here said that mails are not screened/indexed for this purpose when I said: "If you are not paying for it, you are the product." They are not giving anything for free.
The data used to show you upcoming flights and purchase info isn't used to advertise for you, its used to show (hopefully) useful reminders.