Long story short: each of them has its usage case, and not everyone has the same usage cases.

GNOME is for the people that want a clean, straightforward desktop

KDE is for the people that want a highly customizable desktop with classic paradigms

XFCE and LXQt/LXDE are for people that want a classic desktop with fewer system resources

Tiling managers are for advanced users that are proficient with keyboard shortcuts and the terminal, and find themselves bottlenecked with the usual paradigm

But, of course, to the GNOME user, there's no apparent point in the existence of the tiling manager, and the same goes vice versa. Choice is something we must be glad to have in the Linux/BSD world, because otherwise we're stuck with dealing with a single paradigm that nobody's perfectly happy with - just ask the people trying to customize Windows 11!