Why does OSX route table contain host routes for devices on the local subnet?

netstat -nr

Destination    Gateway      Flags    Netif Expire

default      192.168.128.1   UGSc     en0  

192.168.128.1   hx:hx:hx:hx:hx:d0 UHLWIir    en0 1191

192.168.128.78  54:hx:hx:hx:hx:hx UHLWIi    en0  795

you’d normally have a route to the entire local subnet as one route pointing to connected interface - at least that’s how linux, windows, solaris do it

is it anything to do with performance as the same devices are in the arp table?