Why Have First Hop Redundancy Protocols?

The Concept of a First Hop Redundancy Protocol is to prevent this from happening

First hop redundancy protocols (FHRPs) provide alternate default gateways in switched networks where two or more routers are connected to the same VLANs

End devices are typically configured with a single default gateway IPv4 address

If the default gateway router interface fails, LAN hosts lose outside LAN connectivity