Network Diagram

ISP to switch then switch to firewall then 2 cables connects to firewall for HA then from firewall to core switch. why corporate choose this way to build office network, why Network Engineer didn’t choose first firewall after ISP then firewall to switch or router?
Please explain me with the help of different different types of network diagram which are possible to build in corporate in terms of Firewall, switch, router, Access point, server etc.