Comment by pndy

XP in early betas released had that slightly upgraded 9x interface called Watercolor [1] and if they'd keep it, surely majority would pick it up over plastic Luna.

Early experiments with totally new theme were rather unpleasant [2] and Watercolor was abandoned in favor of more familiar 9x looking theme as an option. W11 still comes with that old 9x widgets look - slightly flattened because of that trend but it's still there buried beneath for compatibility reasons. And I'm pretty sure they won't escape with that like Apple did with Aqua away from Platinum.

[1] - https://betawiki.net/wiki/Watercolor

[2] - https://betawiki.net/wiki/Windows_XP_build_2416#Gallery