I would argue, that a preamp adds a certain coloration (at least in case of going direct with dCS gear), that some people may prefer.
I was able to voice a system to my liking going amp direct - it is definately more tricky (one less component and one less pair of cables to alter the sound) but it is perfectly doable. I have sold my ARC Ref 3 (which was their top of the line pre back then) after I tried going direct and never regreted the move.
I have tried several preamps along the way, just to make sure I'm not missing sth, including well regarded SS (Spectrall 30SS) and tube (Kondo M-1000mkII) designs, but in the end I still prefered going direct.
And if you think how can you reinvest the money you have just saved going direct (a pre, an extra PC and an extra IC) ... there are quite a few possibilities.