Those that implemented the unused variable feature are completely unaware that there are two modalities of programming: exploring a problem space, and building a solid product.

When you're exploring, you don't want your compiler to stop you in your tracks to warn you about pedantic nonsense. It's not a syntax error that prevents your compiler from understanding, it's just arbitrary restriction that the compiler decides to pester your about, a sort of a robotic grammar nazi.

Computers are obtuse, the worst thing they can do is ignore your perfectly parseable and valid instructions for arbitrary reasons. Machine, if you know I'm not using a variable, kindly let me know and carry on doing your job.