I wouldn't describe that as groupthink. Groupthink has a fairly clear definition and set of symptoms, well, clear by psychology standards anyway:
https://en.wikipedia.org/wiki/Groupthink
What you're describing doesn't have any obvious "out" group in it. I think instead what you're describing is what you'd expect to see in an environment where judging the merits of tools or processes is very hard and requires a lot of experience, which may be lacking. In such an environment it's natural to look to very successful companies and just copy whatever they're doing, even if you don't fully understand it, in the hope that it works out. And sometimes it will.
This isn't helped by the massive expansion of the developer workforce over the past decades, the fact that experienced people tend to get promoted up into management where they lose touch with coding and become 'architects' working entirely in the abstract, the fact that it's almost impossible for firms to correctly match team sizes to the amount of work required resulting in frequent periods of either overload or boredom (that then leads to reinvention of the wheel simply to find something interesting to do).
And yes, finally, fashion plays way too large a role in things these days. If I had a dollar for every time I read a blog post along the lines of "we had entirely generic serving problem X and we had to pick between Rust, Node or Go", with the far older and more mature .NET/Java stacks not just discarded but entirely unconsidered, I'd be a rich guy. We end up locked in a vicious circle that works against maturity of tools and processes:
- Profitable but slow enterprises look at startups, envy their ability to get things done and wonder if it's because of the stodgy old tools/processes they use.
- Fast but money-bleeding startups look at enterprises and say "we aren't a stuffy enterprise shop so we'll do whatever cool thing I read about on hacker news the other day" and often end up boxing themselves into a corner with immature tools or business approaches. Eventually they (might) turn into big slow companies themselves, often entailing either a rewrite along the way to use more traditional tools or absurd investments into digging themselves out of technical debt (Facebook's PHP runtime efforts being a case in point)