Why the new kernel does not show in GRUB menu post update?

Issue

• After doing an OS upgrade from Red Hat Enterprise Linux 6.7 to 6.9, the newer kernel doesn't show up in GRUB menu even though the latest kernel packages are installed on the system and the entry for the latest kernel is also present in /etc/grub.conf file.

$ cat installed-rpms | grep kernel-2
kernel-2.6.32-573.35.2.el6.x86_64                           Wed Nov 23 19:42:57 2016
kernel-2.6.32-696.23.1.el6.x86_64                           Thu May  3 13:40:16 2018      <---------------Latest kernel is installed

hiddenmenu
title Red Hat Enterprise Linux Server (2.6.32-696.23.1.el6.x86_64)      <---------------------------------Update kernel entry in grub.conf file
    root (hd0,0)
    kernel /vmlinuz-2.6.32-696.23.1.el6.x86_64 ro root=/dev/mapper/rpool-root rd_LVM_LV=rpool/root rd_NO_LUKS rd_LVM_LV=rpool/swap rd_NO_MD usb-handoff nmi_watchdog=0 SYSFONT=latarcyrheb-sun16 LANG=C KEYBOARDTYPE=pc KEYTABLE=us  rd_NO_DM crashkernel=256M biosdevname=0 intel_idle.max_cstate=0
    initrd /initramfs-2.6.32-696.23.1.el6.x86_64.img