Someone had the smart idea to re-write the taskbar and when they did, they did the modern take where they tried to strip every feature they didn't think was important enough to stop someone from buying the upgrade. Over the last 3 years a hand full of features have come back but even those re-implementations have been a poor replication at best.

I'd put a dollar on it being due to tracking mouse behavior — if they want to cheaply track clicks & movement for the sake of advertisers, their surveillance needs to be as low-powered as possible.

Windows has lost UI customization in every release since at least XP. RIP hotdog stand.