It's mostly a problem of authors not understanding what swords *are*. As in, what are they, actually, when discussing what weapons are made to do. Different weapons are used for different, entirely practical reasons within the periods they emerge in.
People stopped using the longsword because having a jack-of-all trades sword was less practical than a one-trick-pony rapier, etc. etc.
If a setting just has a bunch of different types of weaponry with no thought given to why that type of weaponry is in use, it will come off as poor creative planning to anyone who actually does care.
For my part, I make this mistake too!
'Because the author thinks it's cool' may be a valid reason for something being there, but it doesn't stop immersion and enjoyment from suffering anyway
Edit: Since a number of people mentioned what their characters use, the character I'm currently writing dual wielded a piece of rebar and a dry-erase marker for one of his fights, so there's that
People stopped using the longsword because having a jack-of-all trades sword was less practical than a one-trick-pony rapier, etc. etc.
If a setting just has a bunch of different types of weaponry with no thought given to why that type of weaponry is in use, it will come off as poor creative planning to anyone who actually does care.
For my part, I make this mistake too!
'Because the author thinks it's cool' may be a valid reason for something being there, but it doesn't stop immersion and enjoyment from suffering anyway
Edit: Since a number of people mentioned what their characters use, the character I'm currently writing dual wielded a piece of rebar and a dry-erase marker for one of his fights, so there's that