It’s not that game dev or even successful game dev requires doing it full-time. It just requires a lot of effort.
There are many successful Indie games that have been created in a part-time or at least not full-time basis. Two examples are Axiom Verge and Stardew Valley.
Many of the Indie games you see out there are the result of a lone dev spending years working on a part-time or at least not full-time basis (they may have a part-time job only during this time).
It takes a lot of effort and it takes a lot of experimenting & fine-tuning to make a good game. Obviously, the more ambitious your goals are for the game (as in overall game scope) the more effort it will take. And that effort translates into time (and / or money if you’re buying assets and / or hiring people to help you).
This is why it is good (IMO) for Indies to focus on a smaller core game experience and / or make other decisions that will help to lower the amount of effort and time required. How much time is actually required to complete your game at the scope and quality level you are targeting is based on your experience, skills and money you are investing (in hiring people to help you, buying readily available assets, etc).
So, you manage those things by scoping reasonably. For example, going back to that idea of focusing on a smaller core game experience we have seen the birth of Tower Defense games. This is basically taking the strategy combat piece out of the much larger RTS genre. By focusing on building only this smaller more focused core game experience Indies can produce a good solid game with much less effort than had they tackled the full RTS game.
Other ways to manage the workload include choosing an art style you can produce quickly. People have taken this to the extreme of the so-called Minimalist graphics using basically colored squares and other simple shapes. Ultra low res pixel art is another good candidate as is going with pixel art with minimal animation or going ultra low poly.
I think probably many don’t agree with this but I think one of the main jobs of a Hobbyist or Indie is in being able to make trade-offs to take something from the realm of impossibility and place into your realm of possibility. Being able to scope properly (small enough) is a big part of that. As is figuring out how to either reduce the need for unique content or choosing a much simpler style that you can produce quickly.
For example, with something like a Skyrim type of game I would use ultra low poly models for everything and possibly even simple cubes, spheres and such. The detail and uniqueness of the game would come from within the game itself in the interaction and gameplay not from the visuals. On the other hand, if my goal was to make a Space Invaders style of game I may purchase some very high quality art and sounds. Or I could keep a monochrome low res pixel art approach to the graphics in exchange for focusing on the “inside”… building out the actual game play adding more to it.
TLDR: Others have successfully created Indie games on less than a full-time basis (check out Axiom Verge and Stardew Valley) and so can you. Do everything you can to manage the scope of work required to complete your game.
