You could treat ransomware attacks with the same seriousness as terrorism since the practical effects are similar, but the key point of terrorism is that it is politically motivated. So a terrorist group could launch a ransomware attack, but not all ransomware campaigns are terrorism.

The meanings of words is important; rational discussion is impossible when people shift commonly-accepted meanings and definitions to suit their agenda. It's an extremely common strategy in politics. And the word "terrorism" already received more than its fair share of this treatment quite thoroughly in the decade following 9/11.