They can get sued. If they work for a company or studio, their artwork is usually copyrighted. Japan has strict laws about that. If their employer or the company finds one of their works floating around, they can get in trouble, and face lawsuits.
Many artists participate in doujinshi groups, or cons. To ‘advertise’ their future prints, they sometimes show samples, sometimes even full ones, that can be stolen. And when they try to sell their artwork prints, they get very little revenue, because it’s ALREADY FLOATING AROUND THE INTERNET, so why spend money for it?
Again, Artists also rely on commissions to support themselves and their loved ones. For those who are seeking jobs in the industry, having one of their drawings floating around can be very detrimental to their chances of landing a job. If their employer has already seen it on the internet, it looses it’s ‘effect’ once they see it from the artist themselves.
Basically, a LOT MORE.
Emotionally & Psychologically
It can make them LOSE THEIR CONFIDENCE to draw more artwork, because people keep claiming them as ‘theirs’
It can make them DEPRESSED AS HELL, and their family and friends will notice.
It can make them feel PARANOID about putting ANY of their works ONLINE.
It can make them lose SLEEP, APPETITE, MOTIVATION and INTEREST in doing what they USED TO LOVE TO DO.
Makes them lose their TRUST in letting foreigners see their art
Makes them UNCOMFORTABLE sharing their artwork AT ALL
Makes them feel so INSECURE that they make their accounts PRIVATE
Makes them feel that the best thing to do to stop the problem is to DELETE THEIR ARTWORKS and/or LEAVE COMPLETELY
Many people do not even think about these things. Posting an artwork is as easy as right-click save and paste. But the people who suffer for it are the artists.
This is why it is SO IMPORTANT to ASK PERMISSION. They NEED TO KNOW where their art is going, WHO is allowed to reprint from them, so they can keep track, and WHICH ARTWORK it is. Because some are OK, while others are not. Communication is the KEY to bridging gaps, and fostering TRUST, and building a positive relationship with ANYONE.
Btw, if anyone wants to add a point on there, feel free to message me, and let me know. I’m just putting this here, because many times, we do not even think about how our actions effect other people.
Edit: THIS is not limited to just Artists. Creators/Scanners/Translators (especially on tumblr) are also applicable to this, for the last two categories. I have some SEEN people STOP TRANSLATING/SCANNING for a certain fandom or group because their translations/scans are often STOLEN and pasted to other sites.