the internet works on sRGB as that's what most monitors have been built to handle in the past.
so, when you upload to the internet, you're seeing sRGB only.
Many photographers will only shoot sRGB as most of their stuff will never go beyond the computer.
Printers also are rare in anything other then sRGB, but they do exist, so again, many will only shoot sRGB
It is likely that if you continue to shoot and edit in that format, that every time you upload to the web, it will likely be converted.
I'm sure not all pages are built this way, and maybe that's what you're seeing, but editing in ProPhoto RGB is probably the culprit.