Rivian's TM-B electric bike

a full suspension e-bike, 500+Wh battery, with a belt drive for $4,500 is honestly a really good deal. There is a shortage of options when it comes to full-suspension bikes that are good for commutes. Compare this to any e-bike with the Bosch e-bike system. The big risk here for consumers if whether they can match the service, support, and reliability that Bosch has. There appears to be a class-2 e-bike option which is something that significantly differentiates it from bikes with the Bosch system.

"Honestly" does not make it a "really good" deal.

It's an e-bike. The competition is stiff, better looking, and better priced.

If they're lucky, this will appeal to university professors and over achieving parents of unsuspecting kids who want a cool bike but got an expensive dorky one instead.

The e-bike market has multiple tiers/segments. This is not priced to compete with brands like Rad Power Bikes, Lectric, or Aventon. It's likely going to compete with brands like Tern, Benno, Gazelle, Trek, etc.

edit: ask yourself why the median new car in the US sells for over $50k when you can easily find cars for less than half that price.