Like others have said, it's just people who want that kind of thing don't do cards any more, they do external "audio interfaces".
I have a Scarlett attached to the underside of my desk with a pair of Sennheiser HD600 headphones and a Monoprice Stage Right condenser mic on a desk stand.
I'm guessing the inner-PC card space has a bit too much of a EM noise problem for people who care about quality higher than integrated sound can provide (which is pretty good these days anyway) and external devices have room for the inputs people actually want.
Does the Scarlett drive the hd600s nicely for you? (I'm assuming something like the 4i4). I'm in the process of upgrading and was looking at a Scarlett audio interface for creating mixtapes with an external DJ mixer.
I was going to use a different headphone amp with the hd600s and a modmic for general listening and calls though. Sounds like I might be able to drop that 2nd amp (I was thinking about the soundblaster x4)
I have a first generation 2i2, I believe, and it is a noticeable improvement from trying to plug HD600 into a random audio jack which were obviously not able to actually drive them properly in general.
You should be fine dropping the additional headphone amp, which I think beyond the Scarlett or similar audio interface will perhaps be different depending on the amp, but not clearly making up for a deficiency in interface power.
I have a Scarlett attached to the underside of my desk with a pair of Sennheiser HD600 headphones and a Monoprice Stage Right condenser mic on a desk stand.
I'm guessing the inner-PC card space has a bit too much of a EM noise problem for people who care about quality higher than integrated sound can provide (which is pretty good these days anyway) and external devices have room for the inputs people actually want.