Why 'multipathd -k"resize map multipath_device"' is failing to resize the map?

Issue

• After extending the size of volume from 100gb to 300gb from SAN. Issued the following commands:

  # multipath -l
  mpatha (360a9800064716863476f7350324a7478) dm-8 COMPELNT,Compellent Vol
  [size=100G][features=1 queue_if_no_path][hwhandler=0][rw]
  \_ round-robin 0 [prio=0][active]
   \_ 0:0:1:3 sdg 8:96  [active][undef]
   \_ 1:0:1:3 sdl 8:176 [active][undef]
  
  # echo 1 > /sys/block/sdg/device/rescan
  
  # multipathd -k"resize map mpatha"
  fail
  
  # resize2fs -p /dev/mapper/mpatha
  resize2fs 1.39 (29-May-2006)
  The filesystem is already 13107200 blocks long.  Nothing to do!
  
  # df -h /data
  Filesystem            Size  Used Avail Use% Mounted on
  /dev/mapper/mpatha     100G   56G   40G  59% /app
  

• Had to reboot to expand mpatha. This is supposed to be done "on-the-fly". Any reason?