Except if you are in a rural area of a developed country, or in practically any undeveloped country. Most of Africa, Asia and South America have abysmal internet connections, and rural parts of Australia (even a few hours drive from a major city) are only able to get satellite internet.
Tech people often fail to realise how divided and limited access to internet actually is once you leave 'tech hubs'.
Twitter, like most companies, exists to make money. If you're busy shaving off every bit you can from your requests, you're spending a lot of money. You're also losing money because I'd expect you wouldn't be serving ads, etc. as well.
Most blogs that exist to make money aren't targeting those without good internet either, so I don't really see the problem.
This isn't just about Twitter, its about making sure if you are helping build a local Mom & Pop Shop's online presence - which is where all business is now days - then you build it in a way that their customers might care about.
There is a world outside of cities, and a lot of people live there. The tech world needs to wake up to that, because those people where Ubers don't go, GrubHub doesn't deliver, they exist (and vote) too.
If they do, companies will be happy to spend time and resources in serving lighter versions of their content. But if they don't, there's no reason, from the POV of a company, to employ resources in something that doesn't generate revenue.
If there's money, there's will.