> But is this not at least partly a limitation imposed by the tools you are using?
Not particularly[0]. It's more about the workflow and representation of data needed to work. To change this would require fundamentally changing the way this work is done, which I'm not sure is possible to the degree where it would make sense.
All of the applications are capable of being used on a single monitor. Windows can be docked, tabbed, hidden, workspaces arranged and saved, etc. It's just that it's not as efficient to work on a single monitor as it'll require significantly more scrolling, panning, zooming in and out, and switching tabs/windows/applications than having another screen to offload and dedicate windows to with the provided real estate. Once you experience having multiple monitors for these kinds of workflows, it becomes a real bother only having access to one. It sounds superficial, but when that's what a large portion of the job entails every little bit helps.
Even when I had multiple monitors, I combined that with virtual desktops to great affect to help focus what each workspace was used for (one for main 3D, one for compositing, one for texturing, etc). They work really well together. If one wished to stick with a single monitor, then using an ultra-wide would be my best recommendation.
[0] There are some areas, where UI's and viewers are written with 8-bit support only, so a 10-bit secondary reference monitor to use with a dedicated output card is required when working with this kind of material 'properly' (accurately, correctly, without dithering, etc). Even when this isn't required, a second monitor is often used as a dedicated full screen viewer anyways so that an image is viewed at 1:1 in its entirety with no scaling artifacts introduced so the artist knows exactly how an image looks.