Bandwidth isn't the issue as much as latency. Those collapsible sections where the content isn't loaded just mean I have to wait 10 times for 20s while trying to read an article, rather than once for 25s upfront.

Wikipedia has a large audience in areas where bandwidth is very much an issue.

Looking at a probably large page (Intel), html content for everything before references is about 250k, which becomes say 50k compressed.

Maybe for first world connections, that could be speculatively preloaded. IP address to lookup country is enough to guess?

Latency is almost always the killer on mobile (hell, on desktop too) rather than bandwidth for web pages.

Which is why we have to play games like forging the user agent to get the full desktop site

What features does wikipedia have besides collapsing sections?

That sounds like the actual problem is the ongoing bloat of useless, unnecessary "features."

If only we had ever invented a way for users (agents) to signal their preferences to remote servers.

What's that, cookies exist? Someone tell people, it seems everyone believes those are just for invading user privacy. (Wikipedia included)