Because it's not real. It's purely for marketing, not for actual wide-spread implementation.
Even in the best of cases, even factoring in economy of scale and all that, a robot like that will cost upwards of €50k at least, probably closer to double that, will require constant maintainance, and the risk of vandalism or accidental damage is really high. And you'll likely need a (skilled) human operator nearby anyway, because the delivery vehicle doesn't drive itself.
The purpose of projects like this is marketing and public perception.
- The company looks futuristic and future proof. That's good to get investors.
- The company looks like they could replace humans with robots at any time. That's good with negotiations with unions and workers.
- The company gets into headlines worldwide. That's advertisement they don't have to pay for.
This robot is not meant to ever go mainstream. Maybe there will be a handful of routes where they will be implemented for marketing purposes, but like drone delivery and similar gimmicks, it won't beat a criminally underpaid delivery human on price, and that's the only metric that counts for a company like Amazon.
Even if you make them in large quantities, material cost alone will be at least €50k. You will need a skilled operator nearby, and constant maintainance, and if you lose even one per year, a regular underpaid human worker will be much cheaper.
These things are pure marketing devices to pacify investors, generate headlines and make unions and workers afraid.