Every customer is different.
For many buyers, just getting to the top of the waiting list is what they want. They want to be the first. If it means putting down a deposit to have the first "option" of buying the next delivered dealer-stock unit, they will jump on board. The customer is happy to be next, the dealer has a fish on the hook [and some of their money], and the salesperson has added another "hot lead" to the database.
Other people don't want to leave deposits unless they know that deposit is getting them a specific vehicle. Some prospective buyers are more comfortable doing that. If the automaker doesn't take orders and goes strictly on dealer allocation, the customer may add their name to the bottom of the list but not leave a deposit. They will get in the database as a "warm lead" or "cold lead" and might eventually get a call from the salesperson, but most likely they will never hear back. They are also free to shop other dealers and buy whenever or wherever they want since they do not feel financially tied to one dealer due to a deposit.
Being in the market myself for a new car, I refuse to go on waiting lists or order a vehicle (tried ordering once when I was younger...never again!). I also will not buy from any dealer that adds a "market adjustment". I always buy from dealer stock. I want to see, feel, test drive the exact vehicle I am considering before plunking down any money. When the right vehicle comes along I will buy it. I don't need a specific color [my only rule is no black or fire engine red], or an exact custom spec of options. My current car will soon be 7 years old. Bought it new in 2015 from dealer inventory at almost $6,000 off since it had been sitting in inventory for 5 months before I bought it [those days are obviously over.] It continues to do everything I ask of it, so no real hurry to replace it aside from slowly going mad from numerous squeaks/creaks/rattles that have developed as it ages.