Google announced they now require fewer ad clicks to trigger the calculation of mobile page speed scores for an ad's landing page. Google wrote "We’ve recently updated the mobile speed score algorithm to require fewer ad clicks in order to calculate a score. This means you’ll now see a speed score for more of your pages."
Google launched mobile page speed for Google Ads back in July 2018. Here is the announcement:
We’ve recently updated the mobile speed score algorithm to require fewer ad clicks in order to calculate a score. This means you’ll now see a speed score for more of your pages. Evaluated on a 10-point scale, 1 being very slow and 10 being extremely fast, the mobile speed score is based on a number of factors, including page speed and potential conversion rate.
Then Google goes on to suggest you look into using AMP to improve your mobile page speed.
So in short, more Google Ads should now show mobile page speed scores in the advertiser console.
Forum discussion at Twitter.