Headphones: provide volume control when using jack input

The headphones have a 3.5mm input jack. But with that input, the volume buttons do nothing. If it’s also impossible to control volume at the source when the output is via earphone cable, as it is with my TV, then the jack becomes useless. I cannot understand what the difficulty is with permitting volume control when the headphones get input through the jack.

[Mod Edit]: Title Modified to Enhance Search Clarity.