Just my $0.02 worth.
There are many reasons why the SEALS aren't advertised as using Busse knives, some of which were covered above by James. Here are a few I've gleaned from my time in the army.
1. Combat equipment is expensive, especially on a "per capita" basis. Imagine, only one grunt needs so much equipment. Multiply that by a platoon and it starts to look expensive. Multiply that by a whole regiment and the costs look prohibitive, especially to the office-bound-procurement-and-supply-logistic-weenies. They could never hope to have such a humongous budget statement approved, so they have to reduce it. Besides, those low-brow grunts are always losing their equipment in the field, better to have a lot of cheap, painlessly replaceable equipment for them to lose. And if they need some good stuff to get the job done properly? Well, that's why we give them paychecks!
(As a side note, toilet seats have a bigger budget per unit because they are a collective item used by a large group of grunts everyday, and so need to be really sturdy to do the job. Besides, you don't bring toilet seats into the field, so they are much harder to lose.)
2. Generally speaking, those
office-bound-procurement-and-supply-logistic-weenies are the chaps who finally decide what to buy for the grunts to use. As noted in their name, they are office-bound, so they don't get out too much. As a result, they haven't the first clue as to what field conditions are like, and don't want to know anyway. (But they do know what a good toilet seat should feel like, being so full of it that they need to spend a fair amount of time utilising that particular piece of equipment.) So they go for what looks good (or mean), claims to be good, and are easy on the pockets.
3. Being already so full of it, they don't bother to ask the real experts for advise, nor do they bother to ask the end user what his needs really are. (They just grunts anyway. What do they know?) Once in a while, they may conduct some "tests" just to keep the grunts happy and make like they care. But in the end, the pocket makes the decision for them. Or occasionally, this being the new age of a kinder and gentler army where everything must be done with a "May I?" and "By your leave" and signed in triplicate and blessed by holy water in an incredibly complicated ceremony before you're allowed to shoot the enemy, sometimes it's better to utilise equipment that just scares the enemy to death, or incapacitates him with laughter, whichever looks better for the media.
Disclaimer: The reasons given above are the absolute
TRUTH designed to make you want to suck a bullet from a gun, or howl at the moon depending on the phases of the planets.