Because those misconceptions can cause significant harm to the self image of men. Western culture in particular is bombarded by pornography of top 1 percentile guys satisfying women for long stretches of time, then there is the porn genre of women making fun of "small penis" guys, but even those guys aren't small, they are just porn small, the vast majority are well above the actual scientific average. Seeing nothing but big penises in pornography, and the only small penises aren't actually small yet are being made fun of by the actresses, these things have an effect on the psyche of many men, especially young men and teens who consume pornography, even those who are above the scientific average. In the 2000's alone the false misconceptions about penis size lead to the rise of Enzyte, a total snake oil product claiming to offer "male enhancement" which was advertised heavily on tv and ended up the subject of lawsuits with the owner of the company ending up in jail. But even today we still have many men who have a perfectly adequate size terrified that they are too small, buying various other male enhancement products and even going to plastic surgeons to get a lengthening surgery or inflatable girth implants. We need to end those misconceptions about size that has lead our society to this point.
I don't know, maybe you're right, can't tell.
But now I wonder if you're below average
Above average, but certainly not huge. When I was a teen I obsessed over my size quite alot, like many teens do. Even though I started puberty young, at like 10, alot of my penis size growth didn't happen until my late teens, I was still growing some down there even at 19 and 20, and because of that late growth, and the viewing of internet porn as a teen, I got extremely worried about my size for quite some time and it really hurt my self esteem growing up. Even as an adult it has caused some self-esteem issues, because even though I'm above average I am tall and broad and it makes me look smaller down there than I often wish I was.