In google’s case, you might be right. However in general what are you expecting the website to say? An explanation of why react was chosen over other languages? Otherwise the reason you have to enable JavaScript on a react website is because the site doesn’t work without it. I see that like complaining that your gas light on your car doesn’t provide an explanation as to why gas is required for it to run.
If you are curious why a lot of sites use languages like react instead of plain html, there are a few reasons. Prior to react like languages, web servers would generate the page, send it to you, and then anytime you interacted with the site it would send you a whole new page to display. I.e. if you opened a popup for uploading a file, it would send you a whole new page to display which is why older sites flicker on basically any interaction. Newer sites that use things like React are downloaded once. It basically downloads the code to make the website and then runs entirely on your machine. The benefit to this is that if you sort a list, open a drop-down, open a popup to download a file, etc. it all happens on your computer instead of some remote server. No need to wait for a server to respond or download a new page, it can update that specific part of the page instead. Some sites are even fully functional offline because of this which is really cool in my opinion.
This makes a far better user experience because everything is instant and doesn’t trigger page reloads on every interaction with the site.
It’s good for developers because it allows code reusability and vastly increases what you can do. Many of the critical features I have on my site are not possible without JavaScript/React. I actually first developed the site using the old style and changed it over to React because of those limitations.
Google could have updated their site to one of these languages to open up new possibilities in what they can do on their site. That or they might be making it more consistent with their other products for maintainability reasons. I find it unlikely that the people who have JavaScript turned off are a large enough portion of the population for them to care about their data but I could be wrong.
It probably logs the error automatically. There’s nothing you can do on your end to fix their code problem in most cases which is why there is no feedback on what you should do…