Because with each single person who decides to run a particular non free software, that's a tiiiiiny bit more vendor lock on, a tiny bit of control lost, of power, freedom, given up.
And when enough people do this, what happens? Look at Google. Look at the post you're on. You tell me - what happens?
He's not wrong at all - it's just uncomfortable. This is a side effect of capitalism or maybe humanity. Its nothing you or I can single-handedly solve, or cause. But we each contribute to it a tiny amount.