Because I enjoy my Fc, I enjoy clearing simple content with a party, hell I enjoy clearing hard content with competent folks. I also enjoy enjoy personal achievement just as much, just because it's an MMO does not mean every bit of meaningful content should require a party. Hell there is solo content now, it's just SE and to be honest most MMO developers think party content requires a challenge while solo content requires a massive ridiculous grind with little or no real challenge.

Now, the rewards for hard solo content do need to take a bit longer to pay off or have other issues to keep it from eclipsing group content. But considering the number of players griping about not having much to do, a limited number of uses per day would allow it to exist without hampering Coil and similar group content too badly.