This is a shockingly common problem
I don't know why for sure, but I think it might be the rope on sale problem. The rope on sale problem is that if you buy a spool of line it seems, or is, cheaper. Maybe you don't mind that it is all the same color, ( which makes sailing harder, much easier with color coded lines), or that the perceived savings is too much to pass up. Or maybe someone gave you some left over line that would be long enough for a traveler line, fender line, or whatever.
The issue is that all of the lines on your boat should not be the same size. They have different functions and different loads, so why would you make all of them the same? I can't count the number of times that someone had a boat that they could not release the main sheet on because the line was too big to fit in the cam cleat on their sheet block. Or the times that they complained about chafe at the masthead with a 9/16 halyards on a 27 foot boat.
My favorite though is a 37 foot boat rigged entirely with 3/4 inch line.... Nothing worked, but the owner bragged that he had gotten all of it for free... I had to get involved to get him down from the top of the mast when the line he was aloft on jammed in a halyard exit on the mast. What a mess.
Run the load calculations for each use of your line, and pick the right sized line, which these days can get smaller and smaller due to higher tech line with higher load ratings and lower stretch characteristics.
In looking at the line selection also take note of the line diameter required by your rope clutches or your winches, cleats (cam or otherwise). Picking the right line for the use is important. It makes the boat sail easier, and allows people to experience less frustration. Also remember not to just replace what was there. Most of our boats are old enough to have had 2 or 5 previous owners that may have found a great deal on a spool of left over line. (There was probably a reason that it was being blown out of stock by the way, it probably was not the correct size for most usages).
Sail safer, and have more fun, size the rope to the use.
Guy