This is really confusing to me, because I always thought “day Guest” meant any person not staying at the resort in question. The policy you’ve quoted would lead me to believe that anyone can park at any Disney resort they wish to dine or shop at, though I know in practice that isn’t the case. What am I missing?
You are correct, that day guest = anyone who comes to a WDW hotel to eat, shop, etc. The main restriction used to be that only people staying at the hotel could park overnight. WDW's written policy has not kept pace with on-the-ground policy. I quoted that policy because it says day guests are allowed to park if they want to shop, but in practice that is no longer the case. Even people staying onsite are mostly restricted to their hotel + the parks.
WDW used to generally allow people to park at the hotels, especially if you were already staying onsite at another WDW hotel, were a passholder, or had an ADR. Of course, if you are a WDW passholder, you'd want to eat at the all the restaurants. Of course if you had the DDP, you had paid for dining entitlements including quick serve food.
Then, more or less, non-WDW hotel guests learned that they could bypass paying for parking by attempting to park at the hotels. WDW got a little stricter. People who were not staying on-property at all were turned away, especially from the monorail loop hotels, BWK, and BC/YC, unless they had a dining or convention registration. Generally, everyone was allowed to park at the mods and value resorts if they came to eat at the QS.
Anyone staying at a WDW hotel was generally allowed to park anywhere on property for the purpose of dining and shopping.
There were a few small exceptions to this policy, like the major holidays and major events in the parks.
For a time, WDW also had a policy of giving people a 3-hour parking limit at the monorail resorts (with an ADR).
There was an added restriction during COVID, because CR has a separate security entrance (shorter wait), people attempted to get dropped off at CR so they could enter MK faster. WDW said, if you aren't staying overnight at CR, or a registered convention/wedding/event guest, then your Uber can't even drop you off at CR, and WDW restricted mobile ordering at CR to ONLY people staying at CR.
For a long time, GF, Bwk, and Poly had overflow parking lots.
Now many WDW deluxe hotels have added DVC rooms. WDW increased the number of hotel rooms, but it appears the amount of parking hasn't kept pace, so now there is barely/not enough parking for the overnight guests.
Generally, the only time I attempt to park at any of the hotels is when I'm a guest or plan to dine there, so most of the time I have a reservation or ADR. I've not personally tested what parking is allowed at all the hotels, but they have decidedly become more restrictive. Onsite guests are no longer allowed to freely park at all the onsite hotels.
Another oddity is that CBR and Riviera are basically the same property, at least where the parking is concerned. The parking is connected by an internal loop. So what's odd is that CBR guests are not always allowed to enter via the parking lot entrance that is closest to Riviera. (Someone staying at CBR has no reason to park at Riviera.)