If you can make a name for yourself, you can do very well. Especially for Magento, I love the fact that I can make small change, deliver it as a composer package, and then (if the code is good enough) see the results on many brands within a few months.

It's hard to get that close-to-customer visibility anywhere else as most "cool" large scale FOSS projects are dev focused, which means your impact on the lay user is less obvious.