Not sure what particular insights. Well here is some example: state management. It is basically split into 2 parts. One part is the actual business object that matters and is a slice of full data on backend. It is a class with methods that take parameters and modify state when executed and broadcasting fact of said modifications so that the UI is aware. Executions of said methods also causing data exchange with the backend using JSON based RPC. Simple example would be Customer with get/set Name/Alias/DOB etc.
Then there are web components and those keep their own state that is limited strictly to presentation issue. For example Currently active form of the application.
It is a big area in general with lots of details and requires way more than a simple post to describe. Unfortunately we do not contribute to open source so can't really share any code.
So structurally the app is fairly simple. Some JavaScript files that are being merged when posting to production and backend server written in C++ accessible through JSON based RPC that can serve thousands of requests per second on single computer with few real cores without breaking much sweat.
1) tradeoffs, preferences, exigencies of use-case
2) devs who conflate their specific use-cases with universal truths
3) fickle winds of fashion affects tech as much as any human endeavor. Right now jQuery is out and React is in
As for jQuery specifically, there has been at least 2 trends militating against it: a wider industry move away from patterns of direct DOM manipulation into virtual DOMs (i.e. using frontend frameworks); and a more widespread acceptance of functional programming techniques while jQuery is inherently "impure"
Using virtual DOM does not give much benefit if at all on modern browsers.
Functional programming is just one of many existing paradigms and not a silver bullet. One does not need to plug every hole with it.
I would note in passing that a description of industry trends is not an endorsement of them. There are lots of reasons for trends beyond pure rational technical strategy.
As for developer pool - when I need to hire subcontractor I've never had problems finding one with enough qualifications in whatever area I would need. Btw all subcontractors I've ever had are remote since year 2000