Ok, so let’s ignore the fact that Muslims don’t care about kosher, and let’s assume that your maximum guess is correct. That makes Muslims 2.2% of the U.S. population.
Evidently the U.S. Jewish population is close to the same. Muslims don’t care about kosher, so I am not going to worry about them anymore. Less than 3% of the U.S. population is Jews. Now, I have nothing against Jews, but is a maximum 3% increase in sales really worth Kosher certification that would significantly increase the price? And note that I am assuming all U.S. Jews care about kosher. The fact is, they don’t. In fact, the evidence suggests well under half do. So we are talking about a potential of maybe 1% increase in sales, maxiumum. From the sounds of it, the cost of switching to a kosher production line would cost way more than 1%. In other words, the additional sales would not make up for the cost increase, and the price of Soylent would probably have to increase so much that they would lose more business than they gained.
In short, the only way Soylent is ever going to be made kosher is if they can find some way to convert to a kosher production line and hire a rabbi at a cheap enough price that the price of Soylent does not need to change at all. I can only think of one way that can reasonably happen. If demand increases enough that they have to find larger scale production facilities, then if kosher really is a priority for them, they might try to find someone willing to maintain a kosher facility so that they don’t have to pay by the batch.
So if you want kosher Soylent, buy lots and lots of Soylent, and encourage everyone you know to do the same!
And to answer the original question: Why is it so important that Soylent be kosher? If isn’t. Soylent is a business, not a charity. Yes, kosher would be nice, but it is not Soylent’s job to cater to every religion that has dietary restrictions. If the goal of maintaining a low price (which in my opinion, Soylent has failed to do thus far) is important to them, trying to make Soylent kosher would be a bad business move, and since Soylent is a business, that is more important than accommodating every religion.
Kosher is a personal choice. It is a religious sacrifice. It would be cool if Soylent was able to accommodate that, without violating their own goals and principles, but it does not make Soylent bad or wrong not to, and it certainly does not obligate them to. And besides, what kind of sacrifice would kosher be, if everything was kosher?