I needed a good laugh this morning. But of course this is pretty bogus relationship. People who drive Teslas make more money than those who drive Gremlins.
My personal guess would be that using spaces is a practical decision and might be more popular towards older, more experienced devs (who are therefore better paid).
On paper tabs sounds better, they're "configurable", you should indent with tabs and align with spaces, yada yada and everything is good in the world.
In practice however it becomes a big mess real quick unless you only work on projects with very good and perfectionist developers who understand when they should indent and when they should align and how they should configure their editors to do the right thing. See for instance the linux kernel codebase, it looks like arse if you don't use 8-space tabs and the coding style even tells you to use that value (it shouldn't really matter if tabs were used "right", except maybe for 80-column limits). So why even bother with tabs in this situation? Do we really care that much about wasting a few bytes?
Therefore I gave up on tabs a long time ago and tell everybody to just use spaces in all the projects I maintain.
Also some languages are "tab friendly" and there are correlations between language and salary; see previous HN posts on the topic.
They explicitly rejected this explanation after controlling for years of experience.
That being said I'd be curious to see "years of experience working in a team", because that's really when using tabs starts becoming tricky. If you're well disciplined and are the only person messing with your codebase the issues I mentioned in my previous post don't really apply.
If you know another variable that explains the difference please let us know.