sorry to say, but https is not an altruistic move by google.
I'm willing to bet that the terms and conditions for both services allow google to reuse use the analytics infomation.
If privacy improves that will benefit the internet (privacy has real costs that don't involve state actors like hackers, etc). Many people, especially in developing countries, are afraid of transactions over the internet and use cash on delivery.
Better security = Greater trust of the web = Higher adoption = More ads.
No different to them working on Google Fiber.
Google should've started way way earlier
The work actually started quite a while back, but the overall ads industry and internet as a whole moves really really slow. Add the mobile ecosystem to the equation, and there is a bunch of issues.
The whole work is a combination of a bunch of things (in no chronological order): 1. Google pushed search ranking changes. 2. Google moved all of ads to HTTPS, and this took some time to make it happen. 3. Apple created ATS to make people think about it. 4. Apple wanted to enforce ATS for non-web content, had to back out. 5. Let's encrypt made access to certs free. 6. Big vendors joined.
Unfortunately, the world is slow when it comes to changes like these, but i am quite happy with the outcome so far.
edit: added context.