I don't see why you would have a PC like that as you are intentionally making your PC quite gimped and weakening the party.),
Well most likely because that's what the dice (+ race/lv mods) gave me.
My preferred creation method is rolling. Sometimes the dice-gods giveth, sometimes they don't. Sure, I'm always hoping to roll super high or even perfectly (perfect btw is the one combo that I've never gotten in 35 years of doing this). But I'm absolutely willing & able to play whatever I roll. Hell, I'll even roll 'em straight down the line.
Sometimes though it might just be a whim. I've been doing this for a long time. I know I can play virtually any combo & have fun - both mechanically & RP-wise. I also know that my exact +/- will not affect the fun of the other people I'm gaming with.
I've also been known to just throw away pts that exceed my vision of a character & take a lower stat.
I might also prioritize my stats in ways that others would not. (f
or ex; I have a PF Cavalier - a very melee oriented class - whose highest stat is intentionally Cha. His 2nd highest stat is a tie between Con/Wis & his 3rd highest is Str {before magic items}. He's built as a leader 1st & foremost. He's very good at it & that's important to RP side of the game being played.)
if player was doing that deliberately in my experience there will be other issues that will crop up later with that player. I have seen this every time. They might be a hard core role player who thinks combat is beneath them (why play D&D then?) or prefers pretending they are a Vampire or some stupid crap or they like Paranoia RPG where screwing with other players is inherent to the system. There are other RPGs and groups for that type of thing. IN every single case those types of players are better off in another group in my experience so you may as well boot them and save everyone some sort of aggravation.
Really, you'd project all that crap onto someone for making a Str.12, Dex.8, fighter wearing Ringmail?
Would it blow your mind if I told you I'm running a Warlock who doesn't have EB?
If you roll stats and roll crap that is different. I have seen PCs with 3 +1 modifiers as their best stats (not in 5E),
So:
A Str.12, Dex.8, fighter wearing Ringmail - fine if rolled up randomly.
A Str.12, Dex.8, fighter wearing Ringmail - not fine if intentionally chosen.
Never mind that both have the same personality, backstory, & potential for growth/RP....