No, the scaffolding the train is hanging from is not able to support a train on top. There's narrow footways on top of it for maintenance but nothing particularly suited for any transport.

Wuppertal is a city stretched along a very narrow and long valley with a small river running along the center. The valley is very tightly populated, the roads along the valley are few and very congested. Faced with tough traffic problems they built this suspension train over the length of the river hovering high above ground level and therefore avoiding all traffic.

Clever solution.

I'd imagine the ride would be smoother since they really only need to level between each support, not the entirety of the rails if they'd been laid on the ground.

It's also just cool and fun. I imagine a decent number of us train nerds end up visiting Wuppertal because we heard about the upside down train.