Damage and harm

"He wanted to start painting again, but long years of hard work had damaged his hands."

Why we cannot use harm here? Thanks!

You could use "harmed." But it seems to me that "harmed" implies a human agent, damage done on purpose by someone.

Merriam-Webster online:

Main Entry: 1harm
Pronunciation: 'härm
Function: noun
Etymology: Middle English, from Old English hearm; akin to Old High German harm injury, Old Church Slavonic sramu shame
Date: before 12th century
1 : physical or mental damage : INJURY
2 : MISCHIEF, HURT

Main Entry: 2damage
Function: transitive verb
Inflected Form(s): dam.aged; dam.ag.ing
Date: 14th century

to cause damage to

synonym see INJURE
- dam.age.abil.i.ty /"da-mi-j&-'bi-l&-tE/ noun
- dam.ag.er noun