pruned nodes cannot act as seeders for IBD(initial block download) of other nodes

pruned nodes become leachers to full nodes but cannot then take the bandwidth strain away from a full node.
because they then are not seeders to offer IBD to others.
pruned nodes effectively put more bandwidth pressure on the remaining fullnodes

full nodes do full features
opting to turn feature off (listening, archiving) makes you less of a service for others, thus providing less of a backbone to the network protocol