Maybe because he was a shady/greedy guy and wanted rich out of the picture to either steal his connect for himself(if it wasnt shared) and gain access to his territory or customer base in addition to his other bases. (Greed)
Perfectly logical as well imo.
If you follow the chain of events, your theories don't really add up.
If you listen to Alpo interview, it all can down to Rich adding a surcharge to coke front to him and Alpo by Alpos connect. When the guy fronted Rich the coke(with Nixon's head stamped on it) it was for Rich and Alpo. Instead of giving it to Alpo for what he got it for he added $3000 a key.
Listen to the interview, it explains every murder.
