Even though Angular2 was released in 2016, there wasn't really an easy-to-follow upgrade path until mid 2018. (ngMigration-Assistant wasn't even released until summer 2018, and people didn't really start releasing in-depth tutorials until around this time.[1])
Since React was released in 2013, it was already pretty popular by 2015 when Angular2 was announced. So a ton of startups migrated from Angular to React in between 2016 and 2019, when it wasn't clear there would ever be a good upgrade path, or that Angular2 would actually develop into a good product.
Now obviously in retrospect there is now a very good upgrade path, and Angular has actually become quite good, but it wasn't at all clear that either of these things would happen for several years. But yeah, I'm sure there is a time effect here, but I think there might also be something more nuanced going on. Like no doubt most of these startups that are selling are 5+ years old, but that still puts us well into the time when React was popular.
[1] E.g.: https://www.youtube.com/watch?v=qeQljCLpR04, https://www.upgradingangularjs.com/
By any metric, React is by far the most popular framework in 2021. It has even surpassed jQuery. [1][2]
[1] https://insights.stackoverflow.com/survey/2021#section-most-...
[2] https://trends.google.com/trends/explore?date=all&q=react,an...
https://www.npmtrends.com/@angular/core-vs-next
But yeah, I wasn't trying to reply that React isn't still popular.
I guess my main point is that I've learnt that there are a lot more companies who find NG a good fit than folks think, but the same factors that make them prefer NG also mean they don't make a lot of noise online. These are firms of principally senior devs in their 30's to 50's, just building shit and taking care of business. I'm not saying they are better, or that NG is better, just that they are out there.