But this doesn't have to limit you to html only websites. 2008 (or 2006) js was perfectly fine for most tasks.
Problem is, light JS and small/optimized images are becoming more the exception than the rule. When devs have ample bandwidth and powerful machines they're much less likely to carefully weigh every dependency and unnecessarily large image.
In my area the ATT only provides internet that runs 18 mbps maximum. Its infuriating when I am browsing a javascript-heavy website at peak hours and it takes forever to load. I don't think HTML-only is necessarily a good idea, but less javascript for basic things that HTML does well anyway is certainly welcome.
I live in a suburb outside of a large metro area. Not at all considered rural. The only internet provider we had when I moved from my old house to this new suburb was Xfinity (Comcast). The ISP I had previously did not have service in my area and after an exhaustive search, the best I company I could find that WAS NOT Xfinity was a commercial DSL line with a dedicated 5Mbps up and down line for the same cost as and Xfinity line with a 400Mbps up and 15Mbps down. It wasn't even close. I also had to have this company install the line which would've been even more money.
In the end, it was pretty surprising how many areas still only have a single choice for their internet service.
The other way around, I assume?
I don't know how many high speed connections a moving train has, but when I cannot load a simple mostly text website, then some people on board apparently are doing other things than I am doing on that shared connection. One hunch I have is, that they are downloading many megabytes of bloat JS libraries, while I am trying to just read some text on a website and have mostly JS blocked. Some more might even be watching movies or running big downloads or windows updates or whatever.
Anyway, one result of bloated websites, even if we have high speed connections in our homes, is that we struggle with the shared connection, like on a train. If every Billy needs to load Facebook, Instagram, YouTube and whatnot, it surely is not going to improve the situation for other people on the train. Of course another reason might be, that the train's connection is bad in the first place.
Some of us do. I think it's important to keep in mind that especially those of us living in tech hubs are in a highly distorted bubble when it comes to tech — for us, things like gigabit internet and 1-3 year old top of the line phones and laptops are the norm.
Beyond that bubble however are a lot of slow internet connections (sub 1mbps DSL is still a reality for many North Americans) as are computers that are either pushing between 5 and 10 years of age or are of similar power to computers that old (think bargain bin x86 laptops and Chromebooks).
Occasionally I'll pull out my circa-2008 Dell laptop (which can still run modern operating systems fine) and use it for a few hours to remind myself of this. It mostly does fine until I have to use some unnecessarily heavy website.