Is it a case of people not being interested in the functionality, or a case of the functionality being so poor that people don't want to use it.
I remember using X to run applications from half way across North America about 20 years ago. To be specific, I remember using it to do image editing in Gimp. Performance was great. Heck, I even used it over dial-up connections to my university. For some X applications performance was fine, though I was clearly using it for less demanding software.
Of course, expectations have changed. Microsoft has acknowledged this by continuing to improve upon Remote Desktop. I love and use the feature, even though I cannot stand Windows. While I use a couple of X applications over the network, for the most part I don't even bother. It's finicky to get working. Even when the fiddly bits are set up properly, there is no guarantee the software will work.
Are you sure you remember it correct? I specificity remember tests we did over ISDN (64kbit/s). Opening KMail (X forwarded over SSH) and rendering changes took several 10s of seconds.
There is a reason NoMachine and X2Go got invented.
Just to clarify: I wasn't using Gimp over a modem.
The ability to run graphical applications across a network may have distorted my impressions, but I am pretty sure I am remembering correctly. The modem experiences were largely things like previewing papers and preparing graphs, neither of which are terribly dependent upon interactivity. It is also worth keeping in mind that many early widget libraries were much simpler than what came later.
I used to use FrameMaker over a 28.8kbps modem and, while it wasn't fast, it wasn't impossible to use. Typing latency was reasonable, but setting up the screen was slow. Expectations were also different back then of course. Running Frame on my 486sx-33 on Windows 3.1 with 4mb RAM would have been a bear, too.
I remember using X to run applications from half way across North America about 20 years ago. To be specific, I remember using it to do image editing in Gimp. Performance was great. Heck, I even used it over dial-up connections to my university. For some X applications performance was fine, though I was clearly using it for less demanding software.
Of course, expectations have changed. Microsoft has acknowledged this by continuing to improve upon Remote Desktop. I love and use the feature, even though I cannot stand Windows. While I use a couple of X applications over the network, for the most part I don't even bother. It's finicky to get working. Even when the fiddly bits are set up properly, there is no guarantee the software will work.