Why are viroids not considered to be a type of virus?

Because viroids usually or commonly appeared and infects only in plants but the virus infects or grows usually in all types of organisms. The virus has a larger size while viroids have a smaller size. A viroid is formed of only RNA or ribonucleic acid, a nucleic acid present in all living cells while the virus is a nucleic acid that can be both DNA or deoxyribonucleic acid and RNA.