We're sort of in an interesting place where I think we're due to rethink what casual means, I think it means different things based off what people find easy or hard to learn. Some games that are sometimes considered really accessible and lightweight seem to come across as harder around the table for us because their play loops require a greater degree of input and maintenance from the whole table to keep up, even while the people who love them tend to insist that its all very natural in play. Meanwhile some games that are crunchier and more intimidating are relatively easy for us because they have looser play loops and twists and complications tend to be player and GM driven, which means we only do them when it feels right, rather than coming up with something when prompted by the system.
Generally, I see game rules as tools to resolve uncertainty in what would otherwise be freeform roleplaying, so I've noticed that the more a game mechanizes social elements and story structure, the more stressed my players and I get trying to run it. I'm the least stressed when the game assumes I'm bringing it in to simulate specific things within the narrative that present problems for freeform roleplaying-- e.g. structuring a fight and determining winners and losers, while making it long and involved enough to emulate the fiction we like, or allowing us to resolve singular moments of casual uncertainty that show up within the story, but may or may not define it. They're pretty consistently things that were harder to do organically in my freeform message board days, because you'd just have to 'decide' how they worked out, which is a tough skill even when writing a novel, how often do people complain about plot armor or broken suspension of disbelief from convenient power ups or whatever?
I thought about this after reading viewpoints about what it means for a game to have rules for something and be about something-- I've tended to see mechanics as being something you pull in when something is hard or problematic to do without them. E.g. your game about political intrigue between medieval houses might have more rules for resolving combat than for resolving talking, because combat, when it does break out, is harder to make feel fair without the rules.
But obviously, other people don't have the same framework for what that most basic level is, or what makes a game easy for them.
Its also interesting, because I've kind of wondered lately about the new player thing, if you started playing say, in 2018, you've been playing for four years, if you started in 2017, you've been playing for 5, 2016, 6 years. Obviously, not everyone is playing consistently enough to make assumptions about how much they've actually played in that time. But at this point, a huge percentage of what we think of as new players aren't really new anymore. What does content for them look like? Are they evergreen casual players? Is there just a churn where the players aren't being retained? Do they seek out games with a different complexity ratio as they gain experience? What's their degree of satisfaction with the things they liked when they started?