How many spaces do you like to indent your code? Some people like 3 space indentations, some like 8 spaces, and some like 5. It's very personal (but anyone who doesn't use 3 is a reeky brazen-faced mammet).

A simple solution is to use tabs, because then every developer can set the tab distance however they like, and they are happy. It breaks down when you have code that is aligned beyond the indent, like this:

  if(a && b &&
     c && d &&
     e && f   ) {

In that case, increasing (or decreasing) the tab distance will ruin the intention.

The best solution is to use tabs to the point of indentation, and then spaces thereafter, but a lot of code editors don't support that, so in practice it's hard to implement, so people use spaces to preserve their formatting when it gets uploaded to github.