Not only that, but they aren't standardised, and Gnome really likes adhering to standards and staying away from anything they consider unstandardised or janky.

System trays really are a complete clusterfuck.

Sometimes the icons have colour, sometimes they don't, sometimes they're minimalist icons, sometimes they're not. Sometimes you left click on them to do something, sometimes you need to right click, sometimes it's both, sometimes they have their own menu UI, sometimes they integrate with the system's, sometimes you can exit an app via them, sometimes you can't, sometimes they give you notifications, sometimes they just do it through your standard OS notification system, etc.

They are an inconsistent mess. And we all know how anal Gnome can be about UX consistency.

Gnome in the past has expressed a desire for a standardised, cross-desktop system tray that fixes these issues, but tbh I'm sceptical it'd catch on. Not because other desktops wouldn't get on board, but rather because app developers will just go "meh, we'll just stick to what we have" and it won't gain traction.