Are you sure they do that? What about players with long-term multiclass goals? What about players that roleplay more than roll-play? What about players that don't take the time to min/max or haven't learned the rules thoroughly enough? What about players that just have a vision, and they do not care? Out of my last five characters, I have played only one that would tend to be called optimal:
- Half-Orc wizard
- Wood elf barbarian
- Stout halfling warlock
- Drow rogue
- Human fighter
But, I like many others, have fun with a vision. I, like many others, also have fun trying to focus on a skill or sub-skill of a class and make that optimal. For example, my wood elf barbarian was incredibly fast. I think by fifth level he was moving 110' per round without using my standard action. He did terrible damage, but he could escape. My halfling warlock never took a spell that caused damage. My drow rogue, while optimal, focuses more of his spells (arcane trickster) and skills on diplomacy.
I can't believe I am a rarity here. Goes back to that framing: Everyone yelling to change it because they only view it through the eyes of min/maxers, and not the eyes of players making CHARACTERS. Which by the way is what 5e refers to the entire Section 1 of the PHB - Creating a character.