Why does Android OS need custom ROMs for OS upgrades? I have a discontinued LG L5 E455 Android phone that came with Android 4.1.2 OS.

I am forced to upgrade the OS because most of the apps I need to install are not compatible with this version of OS, according to Google Play.

I tried to upgrade the OS through the update option in the Android interface, it did some magic but the Android version is still the same.

I could not find any LineageOS ROM that was created for this phone.


Is it only possible to upgrade the Android OS by a custom ROM? If so, why?
Is it possible to install the official Google versions?
Why does it not work like in Linux distributions that can be installed on almost any PC?
Your phone is from 2013 - quite old to be expecting software updates. Hence it's quite unlikely that you would get a major Android version update from LG (maybe security updates if you're lucky). Custom ROMs are maintained by their respective devs giving a bit of extra life for your device. 

As for the third question, the answer here is very compehensive - Bootloader/BIOS, flashing ROM and correlated risks. Why Android devices are more brickable than PCs?