Second, trade and technical publishing are completely different markets. You need a literary agent to even sit at the table in trade (or traditional) publishing. You also have no chance in hell of getting one ("querying" is a waste of time) if you don't have preexisting connections or have a trendy "hook".
Plus, the objective functions are different. If you write a technical book that only sells 10 copies per month (I'm assuming 0.25% of visitors buy, although that might be on the high side) but it improves your career, you win.
Fiction authors, on the other hand, are trying to make enough in royalties to live on. You'll get about $3 per copy in royalties. You need to be targeting a large audience to even have a chance. Large audiences mean lots of competition; other people out there can hire publicists or somehow have the connections ("querying" agents is a waste of time) to make it in trad-pub (which is deeply flawed, but they can sell books when they get their shit together). If you sell less than 1000 copies, you're done--for good. Your name now has negative value, but no publisher (or agent) is going to touch an anonymous pen name (no platform, no photo with the family and the dog) either.
In traditional publishing, you have to make it a full-time job or you will be flushed out of the system (but they don't tell you that). Most of the time isn't spent on the writing (as the quality of much of what's produced these days shows) but marketing. Your "advance" is basically your marketing budget--they can't force you, but "eating" your advance instead of spending it to market your book (the publishing house won't) is frowned upon.
In self-publishing, there are no rules, but it seems that the successful self-publishers, on average, spend even more time on self-promotion, which writers famously dislike doing.