I will try to answer the question as best I can, but am just learning about the Hebraic roots of our Christian faith so I probably am not as well versed as I should be. (But I can definitely say that it is NOT because people are looking for a replacement for Easter and Christmas - although the RMCC instituted those two holidays as a replacement for Passover and Hannukah.) As I understand - the observance of the feast days is not only commanded, but our Lord, His disciples and the early church observed them and no where were we told to not continue. Also, the feasts are prophetic - the Spring feasts were fulfilled in Christ's first coming and when we observe them, we declare His birth, death and resurrection and the Fall feasts will be fulfilled with His second coming, so in observing those, we declare His return and coming physical kingdom.