It was probably the customers who demanded the weak default password too. Anyone who has ever developed a system like this knows that the users are basically morons and won't be able to look up the default password in the manual (which they lost years ago) and will call your tech support line instead.
I used to write software for fire alarms and the customers demanded the default password on everything (which was the first four digits of the manufacturer's phone number, back in the late 80s before the great re-numbering). Often they wanted a sticker on the damn alarm panel with the password printed on it, preferring instead to rely on locking the cabinet with a key. The fire alarm panel could control various vents and fans that were designed to extract smoke from a burning building, but people liked to use them for day-to-day climate control as well.
Most people don't care about security. If they get hacked it's someone else's fault, they are the victim. They just want an easy life and cool breeze in the summer.