Why doing S-ON is so easy? Why doing S-OFF is so painful and costly?

I have an AT&T M8 m8_ul_ca. I bought that from a chinese people.
The device had S-OFF when I receive, but I do S-ON for flash stock ruu.
I did not know the S-OFF device has more flexibility to flash kernel, radio, custom roms etc.

I do S-ON with these commands

Code:

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adb reboot bootloader
fastboot oem writesecureflag 3
fastboot reboot-bootloader

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why doing S-ON is so easy?

After a while I want to get back S-OFF. I do some research and WHAT! doing S-OFF costs .

What these developers do to doing S-OFF exploit? and WHY there is no alternative?

Download from this link