While I'm all for family togetherness, and certainly it seems only common sense that one might need to 'hold onto' an infant, a small child, any person with mental or physical disabilities, etc. the rest. . .well, I don't truly know.
I'm 53. My Catholic grandparents came over from Germany. Married over 50 years, they never 'held hands' at any point in Mass though certainly there were gestures of affection that were more subtle--Grandpa helping Nana with her coat, Nana adjusting Grandpa's scarf, his hand under her elbow as he helped her walk out to the car over slippery sidewalks. Maybe the "German side'" of the family, especially in the 1950s and 1960s, just was not so 'publically demonstrative' as other cultures. Inside the home we hugged and kissed goodnight, held hands around the dinner table as we prayed the blessings. . .but there was a clear and distinct (and well understood) separation between behaviors that were acceptable and praiseworthy in ONE place (like home) but not acceptable in another (public places including church).
I grew up with first the "Latin" Mass and then the vernacular. I saw everything from the "say the black, do the red" of my youth to the wildest possible 'interactions' in college (yes, I have witnessed liturgical dance, being up around the altar, the 'wave', hugs and kisses and we are SO into the liturgy and we love to add on kewl things like Native American chants--whether there are any Native Americans in our area or not, "Father/mother god", ad libbing the prayers, father doing standup comedy with the microphone, you name it. . .)
Why did it happen? I don't know. Why did people suddenly go from ritual (written out and done in uniformity of posture) to a free-for-all where (it sometimes seems) that the only thing not accepted is simply 'saying the black and doing the red' and that if you AREN'T engaging in anything that 'came about' only in the last 40 years, you somehow aren't 'fully participating?" I don't know. I wish I did.