The documentation can be published in advance of the product launch.

Intel and AMD did this in the past for their CPUs and accompanying chipsets, when any instruction set extensions or I/O chipset specifications were published some years in advance, giving time to the software developers to update their programs.

Intel still somewhat does it for CPUs, but for GPUs their documentation is delayed a lot in comparison with the product launch.

AMD now has significant delays in publishing the features actually supported by their new CPUs, even longer than for their new GPUs.

In order to have hardware that works on day one, most companies still have to provide specifications for their hardware products to various companies that must design parts of the hardware or software that are required for a complete system that works.

The difference between now and how this was done a few decades ago, is that then the advance specifications were public, which was excellent for competition, even if that meant that there were frequently delays between the launch of a product and the existence of complete systems that worked with it.

Now, these advance specifications are given under NDA to a select group of very big companies, which design companion products. This ensures that now it is extremely difficult for any new company to compete with the incumbents, because they would never obtain access to product documentation before the official product launch, and frequently not even after that.