developers who only know how to write fat JS frontends
Nearly every web app is now two apps, and it's increasingly infeasible for any developer to have a mastery of both backend and frontend stacks.
Not necessarily a terrible problem when you have dozens of developers, but a lot of dev teams are 1-3 people. Instead of web dev circa 2010 where you might reasonably have a 3-person team of people who can each individually work anywhere in the stack, now your already-small team is bifurcated.
In many ways this is an inevitable price of progress... 100 years ago you had one doctor in town and they could understand some reasonable percentage of the day's medical knowledge. Today, we can work medical miracles, but it requires extreme specialization.
At least in the development industry, we can choose not to pay that price when it's not necessary.
The front/back divide also existed back then, with barely any possibility of a front person ever touching the back-end (a possibility that exists nowadays, without going into its merits or demerits).
For a reasonably ambitious and industrious individual nowadays it’s not unreasonable to become really good at one client and one server technology. There’s more to it than writing server-side code with HTML templating for presentation, for sure, but it remains well within the grasp of many people.
Because the stack in the old days was smaller and level of quality was far lower. In the '90s there was no css and javascript, nor did anyone care for accesability, multiple languages, security or interactive features. In the old days we had real documents with links and simple structure, not apps and mature frameworks. It was something on the level you get today with simple markup like markdown or org-mode.
There was not "frontend" and "backend" developers. There were designers and developers. Designers created designs. They were usually delivered as PDFs, because the bulk of them came from print design backgrounds.
Their designs were then implemented by developers. Senior level developers tended to more of the application level heavy lifting (server-side scripting & db), with junior level developers working on converting designs to html, then to templates. By the time a junior developer moved on to app code, they were well versed and had mastered HTML and all the weird edge cases. They knew HTML.
The first real wave of "frontend" and "backend" developers came on the scene when you had designers learn Flash. They started driving more complex applications and there was a more bifurcation.
Granted even in small teams of the era, you had developers prefer "front" or "back". We tended to value "A jack of all trades is a master of none, but oftentimes better than a master of one"
In any case, discussions around front end frameworks and especially React are scarcely any better here. Although they are usually politer at least.
Source?
This isn't true, Twitter is a place where a large percentage of Twitter users who are interested in web development talk about it.
Twitter is not a lens on the entire internet, it is a lens on a bubble of a bubble.