Now I know how to do ssk and this isn’t about how to do it. I would like to know why if you do an ssk that you don’t just knit two together through the back? I know if a stitch is twisted you knit it through the back door. I tried ssk and k2tg through the back and they look the same. Is there something I missed?

Apparently for ssk, both stitches are twisted, each one. For k2tog tbl, the two stitches are twisted as one.

It depends how you knit. If you knit combined (wrapping the purl sts the opposite of how you wrap a knit stitch) and k tbl normally, then ssk is the same as k2tog. K2tog tbl twists the sts, but by slipping them separately, it reorients them so when you knit them together, there’s no twist and they lie flat.