Why is this part of the ssh command:

… -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null'

Wouldn't it be better to let the user configure this in it's ssh_config instead of generally using it and thus weaken the security?

From the man page man ssh_config:

CheckHostIP
If this flag is set to “yes”, ssh(1) will additionally check the
host IP address in the known_hosts file.

and

UserKnownHostsFile
Specifies one or more files to use for the user host key data‐
base, separated by whitespace.