You might think so, I thought so too before I started. "I'll just show some pics with text, that's easy enough."
But then I only considered the "creating assets" part of the process - that I save a lot of time using existing pics or vids. Sure, but creating content is so much more than that.
I spend a LOT of time on these updates. If you want to have assets (pictures/vids) that match the story and are as consistent as possible, which is something I'm aiming for, you need to spend a lot of time finding them, getting them and then even when you have them you need to remember what you have, looking through them and finding what you need. At the same time you need to fit the story to what you do have since you can't make up pics/vids that don't exist (I can't render them). When I'm sitting there creating content there's constantly a lot of thinking, what can I write with the assets I have access to, and what assets do I have that would fit with this thing I want to write. Then writing the text and fixing/preparing the assets, which all takes a lot of time. The hours fly by. Then I don't even count the hours when I think of the game and story plots when I'm not at the computer.
I have no experience with creating a game with rendered images, so I can't say which is more time consuming, but it's obviously much easier to write the story and putting everything together when you can create the assets you want, in a way that I can't. Then creating the actual scene to be rendered, yes I don't have to do that. That's my big time saver when it comes to work. But on everything else I'd say it takes me longer (not counting waiting for rendering as work).
Plus, at the same time I have been building my own engine, taking it from a demo version to the current state and there's more to be done. So there's a lot of programming being done behind the scenes, apart from programming the actual content.
I could never do this if I didn't have a lot of free time.
Edit: And btw, for those who didn't know, I had to take it very slow for about a month because I hurt my back pushing myself too hard when finising v0.2. That's why it took so long to release v0.3. I didn't charge my patrons for January because of that.