Orexin-A is available for mass-market consumers to purchase. Nelson Yee pointed out a vendor in his answer, and with a quick Googling, I identified at least three other ones. I think your question is better re-framed as "Why isn't exogenous orexin-A currently widely used by consumers?"
There are a few practical reasons peculiar to the chemical nature of orexin-A: The peptide chain is a bit longer than other peptides more widely used by consumers, and this is one of the characteristics that make it inconveniently fragile. You must mind the need to keep it potent--safe from degradation--from the moment it is created until the moment it is administered to the body, considering the especially fraught moments of shipping and consumer-end storage. Failing to keep the peptide in temperature-controlled, sterilized, bacteriostatic, de-ionized water not subject to physical agitation risks orexin-A's being useless by the time it is consumed, and the shelf life will be much shorter than most consumers expect of their bio-active supplements.
Apart from that, as you can see from the vendors' listings, it is very expensive. Relative to other less direct orexinergic solutions, the cost is probably too much for the casual user to justify.
Another practical concern is that as a relative new kid on the block in the eugeroic market, we haven't sussed out important details like optimal dosing, timing, and drug interactions.
As for why no large pharmaceutical companies have adopted it, I suspect it has a lot to do with the economics of drug development. Consider the following comments from a forum user elsewhere who got in touch with some of the researchers conducting the seminal studies illustrating orexin-A's effects:
Neither Dr. Siegal nor Dr. Baier seemed very optimistic that a pharmaceutical company would bring the hypocretin nasal spray to market in the near future. The reasons (listed below) were all primarily economic. I've elaborated on them, but each point was mentioned by one or both doctors. I'd like to point out that both doctors have been great allies through their research and seemed very disappointed about the lack of commercial interest.
- Target Market is Too Small: To a pharmaceutical company, there aren't a lot of us to serve as prospective customers for treatment.
- Hypocretin is Unpatentable: The molecule can't be patented and the delivery system wasn't developed in a way that it could be patented without special exception by the FDA. This means that any group with the necessary certifications could potentially make it.
- Hypocretin Antagonists Seem More Profitable: While hypocretin itself isn't patentable, a synthetic that prevents it from doing its job is patentable. Several pharmaceuticals are developing antagonists to help insomniacs go to sleep. I wonder if they're aware of Dr. Baier's study on how the presence of hypocretin helps stabilize REM sleep.
- It's Expensive: Getting regulatory approvals is generally a very expensive process that requires multiple human studies, trials, etc.