This thread quotes Keith Baker as saying Wizards wholly owns Eberron. Keith got paid pretty well for it – I believe the Setting Search prize was $100k, in 2002 money, plus I'm assuming he's been decently compensated for the work he's done as a freelancer for Wizards since. And Eberron isn't just Keith's baby – there's a lot of James Wyatt and some of Bill Slavicsek in the original book as well. Keith has never to my knowledge complained about unfair treatment by Wizards – the closest I've seen has been the Patreon post quoted in the thread above, where he laments that unrelated actions by Wizards has made him consider severing ties.I wouldn't take someone non-authoritative's word on that. Do you have some proof on that like a statement from WotC?
And this page talks about Ed Greenwood selling all rights to the Realms to TSR for $5k in 1987 dollars (well, $4k for the material and $1k for work as a design consultant).