Seems to me there are a few reasons for this.
The first is that sometimes seemingly trivial things really do matter.
The second is that some devs lack empathy and can't understand other's preferences.
Following on from these, to non-techies the one can look very much like the other.
Bad devs will often argue personal points on genuine trivia because it makes things nicer for them personally, and since there are likely few real world consequences they don't have to worry about being wrong. Or they just can't tell the difference between important and not anymore having found the things they previously didn't care about actually did affect the project...
Good and great devs will often still argue trivia for the reason outlined: non-techies and bad devs often can't tell the difference, and being seen to be knowledgeable in general can establish them in a position where they can improve the project as a whole, rather than deferring to bad or mediocre devs who would create an inferior product.