Vishnu Avatars like Rama and Krishna get worshipped in all main regions of India. But why doesn't Parashurama get worshipped that much? Is there some reason for it? Parashurama is the longest-serving Avatar of Vishnu. He is even said to be living in the mortal world and will train Kalki avatar. So why doesn't he get worshipped that much?
All forms are His. He promised to descend to earth to save the nobles and to punish the evil when ever required, in this process He either takes a form on His own or influence(may give power) someone to act on His behalf or He may wish to put His amsa (a part) in any being for the cause.
Each avatara is meant for different purpose and the way of worship to that deity and the return we get out of it differs among! Each deity in various forms worshiped in various ways blesses with different results! (like Ganapathy worshipped as lakshmi ganapathi, natya ganapathi, maha ganapathy, arka ganapathy...)
The rishuis (Seers) on doing exhaustive worship on a deity understands these and teaches to the fellow people whom to worship, how to worship for a specific purpose. So wrong way of worshiping may give wrong results by any deity.
Parasurama amsa(a part of avatar) is just limited to kill the evil kings, parasuram later approached lord dattatreya for liberation, parasuram is not purna(complete) avatar.