Ignorance, misinformation, biased, and Urban Legends, of course.
Here in the United States of America, the .38 Special cartridge has a reputation as an effective round which has served both civilians and law enforcement for decades. Whereas unfortunately the .380 ACP has a reputation as an ineffective round used mainly in cheap Saturday Night Specials (Röhm Gesellschaft) as well as the infamous Ring of Fire (Bryco/Jennings) guns.
Also, there's no shortage of tall tales which come courtesy of someone's "father's brother's nephew's cousin's former roommate" regarding the .380 ACP's physics-defying failures in when the bullet it stopped by everything from Winter clothing to skin. Basically, the polar opposite of the .45 ACP's legendary stopping power which tossed enemy soldiers 20+ feet backwards and left bowling ball sized holes in them from WWI onwards until the dreadful day that it was replaced.
Outside the United States, .380 ACP tends to have a better reputation where it served in various Militaries and Law Enforcement agencies clear into the 1980s.