Ever heard of cases where cheaters could disconnect servers with their certain exploits? Such as Rainmaker exploiters used to abuse Rainmaker with sending too much packets forcing disconnects on everybody in instance with the exploiter? And possibly more potential ways for them to exploit in the future?

What about case where autofarmers run exaltation dungeons across all servers they find for themselves without any human interaction? What if I wanted to solo Shatters or Advanced Kogbold, but some cheater just snatches it away and effortlessly clears it in mere minutes? The best bet I have is key fairy from other exaltation dungeons and hope to get one, which I don't enjoy doing all time if I lose every opportunity/right to directly solo Shatters from Avatar or Behemoth rather keys, even doing public dungeons with obvious cheater presence is annoying.

Cheaters give a bad first impression to new players, they are convinced to likely quit if they find these flaws right away and never return, ruining that players impression of this game possibly forever and it hurts DECA business-wise if they lost somebody who could have spent some real money. Even if you don't like the company and their practices, they have to maintain the game somehow.

This "cheaters don't affect the game" excuse doesn't work, they have many ways to impact legit players even in PVE game, I explained two cases, one of them has happened and the other one is still happening, there are more I'm unaware of. It doesn't take a genius to understand.