I would say it's because generally speaking many have come across people saying they are using Ki and found them to be ineffective. They thus equate these experiences with Ki Aikido. Think about it, how many have you met?
In any Ki or chi activity there are many who are for want of a better word'airy fairy'
Yes, I have met a few who fell into this catagory, however I have met some who are very good. So it is pretty much a unfair gereralization you think? So you don't think KI Aikido aikidoka aren't as proficient performing waza/ thus translating it to a very street effective self-defense style, as compared to maybe Aikido organizations under the umbrella of Aikikai?
May God bless!