Primarily because most hackers don’t practice or study design.
As a further reason, consider an instructive metaphor: if you asked a blacksmith why he sucks at writing, his answer would probably be “That’s not what they pay me for.”
As a further reason, consider an instructive metaphor: if you asked a blacksmith why he sucks at writing, his answer would probably be “That’s not what they pay me for.”
[1] https://www.gatesnotes.com/Books/Mindset-The-New-Psychology-...
Except design is far more relevant to programming than writing is to smithing, particularly in FOSS where programmers are often also the ones designing the UI for their applications.