Frankly, I can't believe...Apple didn't add a fan to the Plus
They did....
They called the resulting machine "Macintosh SE"
...
It didn't make sense to go through and redesign the Plus, since they knew they had this other machine in the works.
There were a number of 3rd parties that offered internal fans for the Plus. They had wires that would clip onto the 12V feeds from the analog board and would mount to the metal frame.
Everybody's a comedian. And if you're not trying to be funny, you're missing the point. First, we're not talking about a re-design, we're talking about adding a fan. As far as that goes the analogue board in the Mac Plus was updated at least twice between 1985 and 87. Second, the M0001 was a notorious overheater and found itself in the shop for repairs quite often. At a time when Apple needed their computers to be reliable adding a fan to the Plus would have done wonders for customer relations. Yes, many third party solutions were available, but how do you say to a customer, "I'm sorry your Mac overheated and died, perhaps you would like to buy a third party fan for it after we repair it?" Or better yet, "we're selling you an under engineered computer, so you might want to buy a fan for it to prevent repairs." That would sure upset me. Also, for many of those repairs, Apple had to eat the cost under warranty, something a cheap, easily added-on fan built-into the sales-price would have significantly lowered. Then, we have the fact that the Plus was sold for a full 3 years after the SE was introduced ... so adding a fan at that point only makes sense.