My experience in engineering tells me that vendors and dependencies come and go and get acquired and all of them develop their own set of problems over the years. I get what you're saying, but you picked projects that are easy to see as popular in hindsight, but not so much in early adoption. Why react over angular? There is a problem with picking vendors outside of just "picking the best" that has multiple elements:

- Age of the company

- Complexity of integration with the vendor

- Stability in early adoption

If you adopt the tech too early, you risk instability during a time where you don't have the size as a business to afford that. Nobody that's a customer of Google is going to leave their contract because it was down for an hour. However your new 20 employee startup goes down for an hour? And you just signed your largest customer yet? And it's because you decided to early adopt some tech because it simply "looks good and efficient?". No thanks, that customer will be looking at alternatives when renewal time comes, if they don't just pay out the contract and leave on you already. And good luck getting funding with that blemish that you blew it by adopting cool new trends.

Okay, so being early adopter at a startup is risky. So maybe you go with something that is "kind of" new, and is being used by other large companies. Great, so you start building, and the feature system grows, and the integration grows, and now some new system comes along that is way better. Think about life before React/AngularJS and people who built systems with plain jQuery. There was a time where that was the hottest thing and nothing like React/Angular even existed. So you pick that and then 3 years later you have piles of jQuery and AngularJS/React/whatever else comes out, but remember the maturity thing mentioned above. So now you watch it grow over 2 years and now you have 5 years worth of jQuery and the amount of work it will take to switch to React/Angular is a year long project. You can't just stop everything else to work on this, so it's 20% of your time, nevermind that it's a moving target as you fix bugs/release new things in jQuery over that year. So now you're maintaining both for a year, and then 3 years later it becomes clear that React is the winner over Angular, and you picked the wrong one! At the time you picked they both seemed pretty mature (Google w/Angular and FB with React). Oh jeeze, do we migrate everything again? And from the business perspective how do you even begin to sell this to the people in charge when it results in no benefits to the end user. And by the time you finish it will these even be the tech you should be using? Or will something else rise up to replace that?

The complexity grows with the integration as the age of the company increases. And adding headcount and expecting to solve the problem just introduces more problems. Now your team size is 10 instead of 5 and standup is taking an hour everyday, do you break it up into other teams? What are those teams called? What if nobody wants to work on the upkeep of the legacy? Why would they as an IC? So now how do you split the work up fairly?

I'm not saying "don't use vendors", "don't adopt early" or "don't vet your vendors", but what I'm saying is the problem isn't the tech. It's the fact that the "obvious correct solution" is a changing answer over time. And the integration and added complexity combined with team dynamics eventually becomes the hardest problem a company has to solve.