That's not really fair. GNOME has been working on LibAdwaita and GTK4 for quite some while to actually have stable and usable tools to make the missing functionalities happen. And they been adding these in a really good rate in the last 2 releases. Until now we really just didn't had the tools to implement a lot of stuff.
If you look across to KDE land, and not to bash on them I love KDE, they've been much quicker to introduce features but then also spent many releases fixing bugs and sometimes completely re-implementing those features to work properly.