Believe it or not, gmail was a much faster cleaner better interface before they switched to Angular, and FB worked much better and was way less buggy and slow before they switched to React. The reason the mega-caps pushed their use was to offload processing power to the client, which saves them server costs. Front end JS frameworks don't solve a problem almost every other company has, hence why they had to be pushed by FB/Google, and didn't grow organically from the open source community.