Ugh. The FR tangent is really something. It also is lacking in context. Forgotten Realms took over as the "default" setting (as it were) after the ouster of Gygax and was the only setting that was supported post-Gygax to the end of 1e aside from from two one-off books (Greyhawk Adventures and Dragonlance Adventures and a series of modules (Dragonlance and possibly for OA—I don't remember if the first OA modules predate or postdate 2e).
When 2e dropped, FR remained the flagship setting (with GH not receiving any attention except to spit on it until From The Ashes, and Dragonlance only getting support for Taladas, the other continent). Then the glut of settings began—though those that weren't FR mostly received only limited-run support (like Spelljammer, Dark Sun, etc.) with only FR getting consistent support.
3e came and made GH the default setting (which, in reality, ensured that the setting had very little actual product support), while FR dominated the scene with a seemingly endless supply of products. Aside from some one-off books, it wasn't until 3.5 and Eberron that WotC supported anything aside from FR.
4e, I wasn't around for, but it seems the default Nentir Vale setting got a lot implied support (but no actual campaign setting book), and then there was FR to carry the day with Eberron and Dark Sun seeing some love.
5e has been mostly about the FR again (though mainly through the adventures), but since WotC has been pushing one-off setting books like a door-to-door encyclopedia salesman.
The Forgotten Realms has been set up for success since TSR first released the grey box with more support than any other setting. Sure, there (especially in 1e) are some great things about the setting that helped made it popular, but to contend that a consistent glut of support, that other settings didn't have, hasn't factored into FR's popularity would be grievously mistaken. FR has been the favored child since it first release and it shows.