I found this site on the subject:
I says there that ///One belief of why meat was chosen is because most people feel that giving up meat (beef and chicken) is an inconvenience. The Church asks us to inconvenience ourselves sometimes to serve as a reminder that they should always have God as a top priorty and pleasures as a lesser priorty.
Another belief is that in many poorer countries, beef is a specialty. For us to give it up, helps us to remember about people who are less fortunate than we are.///
I also found this site from Ewtn:
Another site explaining fasting etc…:
Hope that helps! God bless!