Which part? The inability to write code that scales, or the arrogance/ignorance about what they don't know? The "arrogance/ignorance about what they don't know

Which part? The inability to write code that scales, or the arrogance/ignorance about what they don't know? The "arrogance/ignorance about what they don't know" part most definitely exists everywhere, including people who work on long-lived legacy apps. Definitely agree with you there, if that's what you mean.