NWA didn't get rid of the the F.C. ice cream service because it costs more than cake (although I suppose packing ice cream in dry ice may help to boost the cost a little).

The reason it was gotten rid of was that serving ice cream sundaes is a labor intensive task, and the bosses would rather have flight attendants give f.c. pax one tray (which has dessert already on it) and then that flight attendant is supposed to scamper to the back and assist with throwing peanuts and drinks at the cattle class passengers.