But they aren't trying to sell replacement batteries for everyone. Their market is aftermarket (stereo, racing, etc...). That F series probably isn't the most common there, and when something fits already then why make the same thing that just fits a bit better? Nobody is forcing you to buy XS, just don't buy one.
Jesus Christ
they have made the the most common sizes and told you what would work you grown no one needs to hold your hand measure your space available and jam in the biggest batt you can and move on