My understanding is that Minecraft exists because Zach refused to takes Notch's suggestions on how to improve it.

So Notch wrote Minecraft, a better version, and sold it. And it worked out really well.

Infiniminer might have sold, but it wouldn't have sold as well as Minecraft.

And Minecraft then brought traffic to Zach (via people wanting to learn about Infiniminer) to drive sales on his other games, which seems to have worked out well in the end.