It's calculated. They want the phone to have sold out. They want you to then want it more because it is. And they want you to wait in line.
And for the seventh time now -- no, this is not true, they want to be able to have supply match demand. They can't just snap fingers and make factories appear. There are only a handful of chip fabs on the planet that can make many of the key components, they literally cost billions of dollars and years to set up, per fab. If Apple could have an iPhone ready to go for everyone who wanted one on launch day, they absolutely would do that. Apple does not need gimmicks to build hype, they are the kings of hype already. Deal with it, you have no understanding of basic business.