AT and the Internet Archive have succeeded in preserving other content, though not all projects are successful. You can see a partial listing at https://www.archiveteam.org/
Even as notorious a "wasteland" as Google+ (a naming I've had some role in establishing: https://ello.co/dredmorbius/post/naya9wqdemiovuvwvoyquq) had many millions of actual active users, and tens of thousands of active communities (https://social.antefriguserat.de/index.php/Migrating_Google%...).
Unlike numerous other shutdowns, Google announced the G+ shutdown well in advance, though they "accelerated" the schedule twice, from "sometime in August 2019" to April 1, 2019, the eventual shutdown date. The tools Google offered for archiving and migrating content, whilst among the best in the industry (an exceptionally low bar), were incredibly insufficient: buggy, incomplete, duplicative, and not readily portable). It was largely third-party tools and assistance -- the Friends+Me Google+ archiver and ArchiveTeam most especially -- that meaningful preservation was possible.
The conceit of large-scale, free-to-use services has been convenience, capability, and trust, the last a point Google explicitly made in its original G+ announcement:
You and over a billion others trust Google, and we don’t take this lightly. In fact we’ve focused on the user for over a decade: liberating data, working for an open Internet, and respecting people’s freedom to be who they want to be. We realize, however, that Google+ is a different kind of project, requiring a different kind of focus—on you. That’s why we’re giving you more ways to stay private or go public; more meaningful choices around your friends and your data....
https://googleblog.blogspot.com/2011/06/introducing-google-p...
That trust has been repeatedly violated.
And in actively opposing archival efforts, Google, Yahoo, Flikr, and others, are violating that trust only so much the more.
In the G+ shutdown, it was the active dismissal, obstruction, and interference of Google and its user-based support team (the so-called "Top Contributors") which were most disappointing. Long-time Google supporter Loren Weinstein made this point specifically and repeatedly:
https://lauren.vortex.com/2019/01/29/googles-g-user-trust-be...
I'll note that this tends to strongly reduce the value proposition of all Web 2.0 / SaaS offerings, given that even the very largest and wealthiest companies are willing to act in this manner.
The consistency of this behaviour and attitude across multiple service providers makes me think that the behaviour and practices are not coincidental or unintentional.