While I can't speak for the person to whom you're replying, I can tell you why it is annoying to me, and that is very simple. In this thread there are basically two kinds of posts:
1. Posts about the physics of why solar on cars is basically a bad idea (or at least a massive waste of money in the face of much better alternatives).
2. "Yes, but have you tried turning your head sideways and squinting at it like this [...]"
For some reason, solar-on-cars brings out the #2 in many otherwise smart people, and it's extremely tiresome to constantly slap down the nonsense. Because, I think, they really, really, really want to believe it can work.
> People are wrong about stuff all the time. Often more committed to worse ideas than this.
Yes, but when you show them why those ideas can't work, using numbers and science, they abandon those ideas.