In the broader scheme of things, AMD is having no trouble selling every CPU they make this year. That's due to a combination of generally high demand for CPUs, Intel's own production problems (which have caused Intel to prioritize other product segments over the desktop CPU segment where AMD's dominance is now clear), and AMD having to compete with many other chip companies that are placing orders for the same TSMC 7nm fab capacity—orders which now require much more lead time than they did at the beginning of the year.
a) based on the 3900, the supply will be coming in the next few months, and the price is right, once that happens.
b) pricing it higher now and dropping the price in 3 months looks bad
c) the pricing has to line up sensible against other chips in the marketplace, both Intel's and also AMD's other chips (including last generation). For many people, they may be willing to wait to get a 3950 at today's MSRP, but would opt for something else if the MSRP was $100 more, and that something else might be an Intel chip.
d) it can be hard to know how much demand is really there --- AMD had to order production several months ago, and their pre-launch planning included an assumption that Intel was going to launch something notable in 2019, which didn't happen.
Having an initial shortage can reinforce the impression that a product is very popular, and the total lost revenue from under-pricing and undersupplying at first is insignificant for a low-volume high-end part.
Especially since these chips are likely already super profitable. The 3950X ($750) is "just" 2x 3700X's ($300) glued together. It's not like the 3950X is showing any particularly good binning or anything like that.