They haven't done many of the changes for fun but because it makes some things work better i.e. using multicast instead of a broadcast in many places compared to IPv4. Enabling and making autoconfiguration a lot more integral. Making the smallest standard prefix /64 (with P2P being /127) - eliminating basically all thinking about how many hosts can I fit in a subnet.
There are things with MTU and fragmenting that are partially more complicated but in a sense also simpler than IPv4.
