Interestingly, one of the smaller, family run, bookmaking-chains [they have only 3 offices in Glasgow], still use a customised version of TV Teletext on all of their information screens. I guess they employ one of their own staff to input all of the up-to-date data as required; it seems to work well.
The text services provided on those other platforms are simply not the same as those provided by digital text services, nor are they all in one place.
For instance, the BBC News site does not provide local Scottish news, or MotoGP news, and the Sky website does not provide a rolling 3 minute news summary, and a similar weather service, or NFL news, just to mention a few.
I recall seeing a Demo of Teletext at the Radio Show at Olympia before it was available on air. It was a useful service in its day but what I found so annoying was if you just missed a page when there were a lot of pages in a selection and you had to wait an eternity for it to come around again, and if the page had a lot of content you didn't always have enough time to read it all.
The remarkable thing about Teletext is that, in the 1990s, I was at an exhibition in the USA where someone was demonstrating a data via TV service on a cable TV network and claiming it was a completely new idea. The sales director had never heard of Teletext even though it had been around a very long time by then.