Tabletop RPGs possess the capacity to provide a wide array of gameplay experiences, exploiting the liminal nature of the medium to seamlessly go from exploring a specific defined space (a dungeon, a valley, etc.) to managing an enterprise (an expedition, a government, etc.) to developing new capabilities (new technologies, new resources, new organizations, etc.) all without doing more than uttering a few words.
It turns out that most gamers don't want that. They want a specific, narrow subset of that potential. They want to repeat the play of that subset. They want to discard everything other that thing they want, which is why they abandoned tabletop RPGs as soon as they found an alternative that delivered on the specific focus they wanted without the stuff that they did not.
The current example that nails this are the horror gamers who prefer to focus on playing "Can I survive this horror scenario?" games, cooperating with others against the monster (or monsters). There are clearly defined play-spaces, objectives, resources, and capabilities for both the monster(s) and the survivors. Play instances go for 20 minutes or less apiece. Play is drop-in/drop-out, and algorithim-based match-matching makes playing the game no longer require having people already at-hand to do so. (e.g. Dead By Daylight, Friday the 13th: The Game
Those gamers don't want or need all that a horror RPG provides, and find that all the other stuff just gets in the way of their fun. To make the RPG into what they want involves hacking up the game into something other than what it is, and as a result satisfaction is never going to surpass what the focused alternative provides.
Games like Diablo focus the greater fantasy adventure RPG down to one character, focused on seeking ever-greater treasure to defeat ever-stronger monsters, and they have to clear ever-harder dungeons to get that loot. They manage few, if any, allied NPCs and don't give two shits about strongholds, politics, or even the lore of the setting. (How many characters with names that, if they were real people, you would regard either them or their parents as insane and dangerous have you encountered?) The part of the game they want, as these videogames show, can be better done when coded into a program; it's no surprise that they quit the table as soon as these arrived.
The key here is focus. Most of the gamers who formerly played TRPGs only wanted a piece of the whole. They enjoyed that thing, and not the rest. Every videogame, boardgame, or cardgame that bled off TRPG players reveals a focus of interest that they wanted without the rest getting in the way of their fun. If you want to succeed in selling tabletop RPGs, then you need to know what those focuses are and why the focused alternative better satisfied that segment of the lost audience.
Yes, this includes things like Visual Novels. This includes games like Civilization and its competitors. Every one of these appealed to those who formerly used tabletop RPGs to satisfy their gaming desires, and until you identify the focused play experience provided and see why it does that focused thing better you're going to spin your wheels.
And no, the answer is NOT to become narrowly-focused in turn. That's one of the big reasons D&D 4th Edition was a pile of shit, and that bad influence lingers not only in D&D5, but also in Pathfinder. The answer is to take that understanding of why those gamers who want the focused alternative do so, and let them go; your audience wants the full potential of the medium, not to tolerate a pile of baggage until they get their itch scratched.
So, if focus is a thing, then what else is there to account for? Tomorrow, more of that.