[Q] About unlock the bootloader. topic

hi guys .I have a V500,and I had flashed the TWRP on my device. And then I flashed a custom rom such as cm11. But ,in my opinion ,many phones flash roms must unlock the bootloader first . and then flash the recovery etc. But why our v500 don't have to unlcok the bootloader ?
Does LG provide the offical bootloader unlock service? Thanks.:angel: