A lot of these were just rebranded hangouts on air became youtube live, Nexus essentially became Pixel, Picasa became google photos, Chrome apps were nothing more than the website, MyTracks as they pointed out is Google Fit
Youtube Live was a distinct product from Hangouts on Air [1].
Nexus -> Pixel can indeed be described as a re-brand or a rename.
Picasa and Google Photos have been separate for years [2][3].
Chrome Apps were exposed certain platform features that there's still no web-based alternative for [4].
[1] http://www.theverge.com/2016/8/15/12490666/google-hangouts-o... [2] https://en.wikipedia.org/wiki/Picasa [3] http://googlephotos.blogspot.com/2016/02/moving-on-from-pica... [4] https://news.ycombinator.com/item?id=12322791
And the big thing with Picasa is the desktop app, which many users are upset to be losing.