You're saving a fraction of a cent per device, while banking on customers not sending it back as defective because it didn't charge when they tried it with a random cable.
If it is a deliberate choice, it's a really, really dumb one.
Advertising is primarily about convincing is to buy things we don't need, don't want, or which are 'stupid' in some way.
Half empty plastic packaging, especially the sort where the company spent money to [re-]design it to deceive people - stupid. It should be illegal. Near ubiquitous.
One of my theories is that there is a deliberate choice happening by people who don't realize it is as simple as a couple of resistors and think they need some fancy PD negotiation chip.
Even over on r/usbchardware it is super common for people to conflate "PD" with this missing resistor issue. Part of the confusion is that the devices that people want to charge with are very likely to be PD power supplies.
If it is a deliberate choice, it's a really, really dumb one.