You have to ask GTK/GNOME developers this. KDE developers go to great length to make their Plasma desktop and all interoperable and that applications made in other non-Qt GUI toolkits still look and behave as best as possible even under Plasma desktop. Looks like GNOME developers do not take care of this and so their interoperability under GNOME is so bad. Not supporting server side decorations is just one of the many many examples of not being supportive and caring for broader FOSS ecosystem.
No I mean why KDE apps cannot have their theme so that THEY arent broken
They are broken on any desktop, decorations are not an issue
You have to ask GTK/GNOME developers this. KDE developers go to great length to make their Plasma desktop and all interoperable and that applications made in other non-Qt GUI toolkits still look and behave as best as possible even under Plasma desktop. Looks like GNOME developers do not take care of this and so their interoperability under GNOME is so bad. Not supporting server side decorations is just one of the many many examples of not being supportive and caring for broader FOSS ecosystem.
Agree with the latter, but not sure if this is the issue
GNOME not being really adaptive makes it very easy to use their apps on other desktops, they just dont look wrong