Are they selling this? If not, why waste effort making a page for it?
Marketing. Lead times for delivery contracts are probably long. Expanding your marketing, making your target audience aware of the product ahead of time, is useful. It makes future sales cycles easier, as your potential customers may already know about your new product.
Hype. Self-driving cars and trucks already have lots of hype, but not usually for the big 18wheeler delivery style. Waymo may need to increase not just awareness but also excitement.
Testing for product-market fit. While a purchaser won't make a decision based on this page alone, Waymo can make some decisions and learn some things based on people's reactions to this.
I could keep going, there are thousands of reasons that making a page for a product or service not yet for sale can be a good idea and not a waste.