Because when I move left in tabs, the cursor isn’t clear which tab I’m on. It also tried to sit off the left edge of a terminal in some editors because it aligns with the right side of the character (the tab), instead of the left.

I do see how tabs are a better option : they allow the one editing the file to decide how wide the indentation is. That’s actually good User Interface design, by separating the data from the rendering layout.

I can see the argument both ways, but I like to use spaces so the visual and editing interfaces are more standard.