Hussar
Legend
Fair question, but the answer is easy.
My concept was (as far as stats go) to have the best Dex/Cha, reasonable Con/Int, and low Str/Wis. But there aren't enough points!
Since I wanted 5/20/12/12/8/20, but there aren't enough points, then I have a choice: either reduce the scores that really matter to me (Dex/Cha) or reduce the scores that don't matter so much. Put like that, why on Golarion would I choose to lower my Dex/Cha?
I'm happy with my choice, but the point is that point-buy gives me that choice (to further lower some scores in order to further increase others) that simply isn't possible with rolling.
If I were simply choosing scores then there is no pressure to get six 18s because I only need 18/18/12/12/8/7 in order to realise my concept.
That's part of the challenge of gameplay (as opposed to the challenge of character creation): play to your strengths and minimise your weaknesses.
Now, some of this is an artifact of the 3e/Pathfinder system. There is a major difference between a 16 and an 18 in 3e, that is largely absent in 5e. Also, I have very little sympathy to be quite honest. If your "concept" requires two 18's in order to be playable, I'm not sure I'm all that interested in that concept. If you cannot honestly play your concept with 16/16/12/12/8/7, I'd put that on you and not the system.