Because, for me, I realized I was the only one at the table with any interest at all in OGL material. Everyone I played with was WOTC only. So, I'm wondering, for someone who professes to refuse to play a non-OGL (ish) game, how much OGL was actually seeing use at your table?
I'm not Cadence, but the answer for me is: A lot.
My players are all using WotC classes, but all of them have equipment from OGL sources and the spellcasters use a lot of OGL spells. Meanwhile, as DM, my use of OGL material is extensive. The books I'm currently carrying to the table are: PHB, DMG, MM, Tome of Magic, Ptolus, Chaositech, and Dynasties and Demagogues. But all of the pre-published adventures I'm using in the current campaign are OGL. And my original prep work is chock full of the stuff. And my binder of house rules is primarily made of nifty stuff from OGL supplements that I don't necessarily want to carry to the table.
For example, a typical original adventure I've prepped for the campaign includes material from: AEG's Evil, AEG's Undead, Creatures of Freeport, Alchemy & Herbalists, Traps & Treachery, Traps & Treachery 2, Necromantic Lore, Monsternomicon, Book of Eldritch Might, Spells and Spellcraft, ENCritters 2, Serpent Amphora, Spells and Magic, Tome of Horrors, Dungeon Crawl Classic 5.5, Kobold Quarterly, Where Dark Elves Rule, and Tome of Drow Lore.
The rich and diverse library of supplemental material that the OGL created for 3.0/3.5 is basically the reason the 3rd Edition has been my primary RPG system for the past decade and a half. It's not just that it simplifies my prep load; it also enriches it with a constant stream of creativity that I can mix and remix with my own. Plus, whenever I'm looking to start a new tentpole campaign, there's almost always some OGL product that's enticing me: Whether it's a great introductory module like Tynes'
Three Days to Kill or Cook's
Banewarrens or Green Ronin's
Freeport or Necromancer's
Rappan Athuk or any of the other dozen D&D campaigns I'd love to pick up and play.
I'm pretty comfortable saying that if it wasn't for the OGL, I probably wouldn't still be playing D&D. I spent the decade before 3E came out swapping game systems all the time. I'm guessing I'd have spent the last decade doing the exact same thing if there wasn't a constant stream of diverse, creative products being released.