Because it gets you excited for jihad. Music is haram but it is only permissible to use musical instruments with jihad music. is this true.the only permissible songs are naats with no musical instruments and jihad music with or without musical instruments.is this true .
All types of musical instruments under all circumstances including ?Jihaadi music? are Haraam.
Hadhrat Abi-Umaamah (Radhiallaahu Anhu) said that Rasulullah (Sallallaahu Alayhi Wasallam) said, ?Verily, Allah has sent me as a mercy for the worlds and as a means of guidance for the worlds, and He has commanded me to destroy musical instruments (flute, etc.) and idols?? (Mishkaatpg.318)
There are other permissible ways of motivating one for Jihaad. That is by inspiring talks and poetry. Anything Haraam cannot be justified even for a good cause.
and Allah Ta’ala Knows Best
Mufti Ebrahim Desai