I'm not sure that this is accurate for all groups. We all suffer from the tunnel vision of "sample sizes of what we experience" ...
I've taught people ... so many people ... to play D&D. And I think that there are some people that find the roleplaying more challenging. But there are also a lot of people (a lot!) that find the rules challenging. D&D has never been the heaviest game out there in terms of rules or "crunch," but it's also one of the heavier games.
As a general rule, a new player can always find something easy to grasp on to. After all, if you are playing a Champion and you are using ToTM, it's fairly easy to grasp. But as soon as you start tossing in spells, or a battle map, or any of the things that require just a bit more ... it can be overwhelming.
And this is before we get into all the ways that D&D has confusing vocabulary or rules. Levels ... as spells? as class? thankfully, we don't use it for dungeons any more. Why is Armor CLASS a number, and what does it have to do with your class, and since it doesn't, why does it share a name? How does stealth work, anyway (I'll get back to you on that one)?
Having seen people learn and play D&D, I can see that we often ignore the ways that people struggle at first- usually because we are helping them! And there are those that never
git gud when it comes to the rules. At least, in my experience and observation.
PS- FKR?
A lot of the time, I fail my own wisdom saving throw. I sometimes will refer to FKR with the assumption that people will know what I'm talking about, given that I've written about it in the past. However, as @Micah Sweet recently reminded me, that is not the case. So, since it has been a while...
www.enworld.org