Maybe because looking up certain manga can be a waste of time or not in line with your interests.
Maybe it's too scary or inappropriate for some people. That could be a reason.
The main reason could be that looking for specific moments out of context might lead to a misunderstanding of the plot. Also, it takes away the fun of discovering things naturally as you progress through the manga.
Maybe it's too intense or scary. Some manga can have elements that are disturbing when you look at them.
Not looking up fiction could be because it can consume a lot of time and prevent us from engaging in more productive or beneficial activities. Plus, some fictional content might have negative influences on our mindset or values.
You shouldn't hold up manga because it disrupts the normal distribution process. Publishers have schedules to keep, and holding them up messes with that. Also, it could potentially lead to legal issues.
It might be illegal and violate copyright laws. Also, the quality could be poor and not give you the best reading experience.
Looking at manga online illegally might violate copyright laws and hurt the creators.
Maybe it's because they can be addictive and take up too much of your time.
Maybe it's hard to find or not widely available. That could be a reason.
Well, for one, teasing manga might hurt the feelings of those who are passionate about it. Also, it can create a negative atmosphere among the manga community. We should encourage and support rather than tease.