For next time: if you don't know how something works (in this case, how linux is developed and by whom), ask! It's better than assuming and jumping to conclusions.
Most linux developers are paid to develop linux. Based on Jonatan Corbets stats less than 15% of the changes could possibly be from volunteers. More than 1200 developers affiliated with ~200 companies contributed to the last release alone. There are nuances here (some developers might not be full time _kernel_ developers) but the argument that linux development isn't professional and mostly paid work has been invalid for years.
