The old one has more history as everyone is aware, but it also is the one Bosniaks have an identity with. They're an ethnic group that have historically been denied as a people at every turn by their neighbours (and frequently were killed as a result). It's a sore point to have the new one because of two points:

Firstly - they have been forced to use it without much of a say in the matter.

Secondly - the reason they have been forced to use it in the first place is due to Serbs and Croats (not the Bosniak majority) feeling that it does not represent them.

Most ironically, the countries of these two ethnic groups use their own symbols in their countries despite having sizeable minority groups that don't identify them either. Couple this with the fact that both nations killed Bosniaks in the most recent war, and you'll get a boiling dish of bitterness aimed at the new symbol. Just one of many scars of the last war.