You are of course speaking only of those from your generation who successfully learned the game and persisted in playing it for nearly three decades. The self-selection here is self-evident. Consider how many people in 1980 might have picked up the game and maybe tried to play once or twice, but ran into difficulty understanding it and so dropped it and never looked back. No internet on which ask for help also means no internet on which you could see them asking for help. They'd have been effectively invisible to you. For all you know, the failure rate for learning D&D was ten times higher back then than it is today..
Certainly, my observations were anecdotal, and to some extent were a product of self-selection, but probably less so than you are imagining. As mentioned, with no internet during that time it is hard to make any observation on this subject that is not just conjecture.
What I can attest to were these observations:
1 - In 1980 interest in D&D swept through my suburban community.
2 - Every member of the local Boy Scout troop got hooked (including me).
3 - That troop included nearly 100 boys ranging in age from late elementary school to high school.
4 - We played D&D on every camping trip and not a single person in the troop had trouble learning the game.
5 - Those Boy Scouts introduced dozens of their other friends to the game, and I never heard a single story about "Joey Smith being too stupid to learn D&D."
6 - D&D became so popular that we played at school during recess and even had after school clubs where even non-geeks joined in the fun with little trouble.
7 - Though the game was dominated by teen boys, we did have some girls join in and learn the game without much difficulty. I even ran some games for an exclusively girl group of my sister and her friends.
8 - Every person that had an interest in the game learned to play with relatively little difficulty. I can remember not a single one of those people having a reputation for being system-inept after a couple of sessions.
9 - The only people that did have any problem learning the game were those that weren't really interested in the first place and only tried the game due to peer pressure.
10 - As far as I know, only a small percentage of us that learned the game back then continued their interest in the hobby through their adult years and are still interested decades later. My best guess would be less than 1 in 10, though I have no way of knowing for certain.
My point was that anybody should be able to learn 5e with little trouble if such a large group of average kids could learn old school D&D with none of the resources that are available today. If I had to guess the contributing factors to this learning difficulty I would think that it boils down to an inability to focus on something for more than a couple of minutes without being distracted by phones, in combination with a lack of consideration for wasting the time of other people, as well as a reliance on hand-holding in place of utilizing their own problem-solving ability.
Obviously, there are bright kids today. I am not calling younger generations "stupid". What I mentioned above was just in support of my opinion that any difficulty learning the relatively simple 5e appears to most likely be the result of societal and cultural differences.
However, there are many reasons that the film
Idiocracy seems to be more prophetic with each passing year, and has become such a well-known meme. If you haven't seen it check it out. It may seem like a dumb comedy at first, but there is a certain genius to it, especially the family tree sequence.
