The answer is because these days people have to find an issue with everything that Disney does. I mean if you can't separate for a few seconds from someone in your party then you have bigger issues to worry about.
It was a valid question and again I will say that people are finding issues with almost anything that Disney does. It is comical to see people get so upset about this. I mean security isn't separating 5yo kids from their parents.
I would not say I am "so upset". It is more like, annoyed and less likely to subject myself again to said treatment.
For me, it is the principle.
I resent going to a relatively expensive leisure destination and then being treated like criminal. I get the metal detectors, wands, bag checks, and grumpy guards. Fine, makes sense, I guess, but it feels really... creepy... to be forced to separate from my family, even for a "second" when I have done nothing wrong. Even the airport doesn't do this, why does an amusement park need to? Hint: They don't. Not at all.
WDW will say they do it for logistical reasons. I say, fix the *logistics.
So, yea, it is not that I cannot be separated. It is, should I be separated? The answer is an easy "no".
In my advancing years, I am increasingly principled. When I was in my 20's and 30's I can tell you I couldn't have cared less.
Opinions will vary.
*Way earlier in this thread I detailed my experience. What I left out, is the gate area is so crazy packed with mobs of people, that if you do get separated from your family by 30+ feet, like the guards demand, you do run a good chance of losing visual of the rest of your party. Logistically speaking, it would not be an issue if the gate crowds were significantly less. Logistics.