You are mocking the leadership of the church's views on what today's youth are experiencing by equating internet porn (instant and free access to sexting, all styles of pornography, easier ways to identify willing individuals for physical or digital sexual interaction) to playboys and VHS tapes
You have no idea what you are talking about and when my teenage and young adult children have the opportunity for virtual reality pornography and farther advancements in pornography, I am not going to downplay how much harder they have it compared to what I went through.
In seconds, a high schooler or recent graduate can have any sort of sexual stimulation they yearn for. Smart phones and the internet changed things and have turned pornography into an issue it wasn't in previous decades.
Edit: If I misunderstood your post, I'm sorry. I couldn't quite tell what you are getting at. The world may have mocked the church's views on pornography over the years you listed, but I don't think many believing members of the church growing up during those years disagreed with the church's stance, they're just addicted and doing destructive things they feel constant compulsion to do
I am 29, active in my single's ward and this month I hit three years free from sexual addiction that I was addicted to from 14 to 26. I used to be very involved with my singles ward's anti-pornography program to share my story and be a voice to addicts that they can change and it is eye opening, when you really get involved with those things, to see how many men in your ward are addicted to these things. My bishop is an amazing man. A number of bishops in my stake are involved in this program. None of them play the "we had porn in the 60s-80s too, ya know?" card. Because it's not the same situation.
So for people in this thread who want to SINCERELY know (not just throw up their hands and say "pornography was around back in 1975 when I was 18 too! It was the same sort of temptation you kids go through. That can't be the reason missionary numbers are low, it's because millennials are lazy and godless!") why missionary numbers are down, do some research, and you'll find out how big of an issue this is to Mormon youth
And if you want to disregard the sexual addictions today's instant access to pornography has caused to Mormon youth, then enjoy the low missionary numbers because you aren't going to make any progress with any sexual addict by telling them "well we could get our hands on playboys. You lot just aren't trying hard enough!" when the smart phone in their pocket can get them connected to any sort of pornography or sexual interaction with a girl their addiction wants, in seconds to an hour.