I imagine that they exist to give struggling players a small extra influx of gold to spend on preparations when they''ve otherwise run dry... say, to try and secure a better chance at the next run. Or maybe they can occasionally top off an upgrade cost. Or other such situations. Even tasks like "Get weakened" and such are going to happen eventually (if you spend time in Ick Swamp, in that particular case). It might even act as a suggestion of sorts, like "Hey, want a bit of extra gold? Well, playing as a rogue for a bit is going to at least get you that "doge attacks" bonus fairly soon" kind of thing.
Going from that assumption, it makes sense that those of us who've become comfortable with the game or who can at least win reliably often don't see the impact at all. I also don't know how my assumption actually measures up to the effect I imagine it's meant to have in practice.