My personal suspicion is it has to do with the sound and mouthfeel of the words. I think -ves plurals happen when it might be hard to hear the difference of and pronounce certain single-syllable words like ‘dwarf’ with just an S on the end. The V might give the plural more weight. Same as words that end in X or S where trying to emphasize the plural S makes it a tongue twister.
The if-you-ask-a-linguist answer is that it has to do with what language the word is derived from. “Steward” and “sheep” are Old English, which is the source of many irregular plurals.
“Matrix” is Latin, which has rules you can learn. “Octopus” is Greek, but its Greek plural is both obscure and confusing in English. Most English “-us” words are Latin, so we expect “octopi”, and in fact this is acceptable. Only pedants say “octopodes”.
As this topic has deviated a little from the original question, I don’t mind sharing a poem about the vagaries of pronunciation in the English language. Apparently, it’s a classic, but I only found out about it today. It’s called The Chaos by Gerard Nolst Trenité.
The general rule seems to be to change a final f to v and add es when pluralizing, but there are plenty of cases where leaving a final f as is and adding s is an acceptable alternate spelling… and other than roof to roofs and not rooves, I struggle to find an example where the f to ves version isn’t found… though it does turn out Firefox identifies dwarves as misspelling.
But bah, spell things however you like, as long as most native speakers can understand what you write, only the most pedantic are likely to give you grief.
Keeping final F is mostly found in French borrowings: chefs, never *cheves. This applies even for older French borrowings that aren’t seen as French any more: chiefs, not *chieves (from exactly the same word as “chef” just a couple centuries earlier).
We also see it when there are two F’s at the end, though this wasn’t always a rule: nowadays the plural of staff is usually “staffs”, but historically it was “staves”.
Stave and staves are still used in various contexts (certainly in British English anyway). It would be rare for me to ever refer to a group of “staffs”, but I do have the word staves in my head for that. But then, I do still use the singular die for “dice”.
Doing a quick Internet search, apparently Americans refer to a musical stave as a staff! Weirdos.
My game will probably have the title “Five dwarves” so I wanted to be on the safe side, but yeah, both writings are ok. It will be a group of dwarves travelling from west to east to face a dragon and his treasure. So, if anyone is reminded of a famous book, well, you are right…
I ran across a good F vs. V plural today, so consider this: if the dwarfs call themselves dwarves, and they have multiple strongboxes that they keep their treasure in, are do they call them “safes” or “saves”?
My English accent is more or less standard American English and this is my shot at the first verse in British English (following the IPA) (as you can see I cannot read IPA very fast):
