This is an excellent question. If it was valid, the question is why it wasn't filed more recently, and what was the aegis for Gail that was against them in filing?
Seems weird. Hopefully good luck to all involved.
This is what I've pieced together from my readings on this and listening to the podcast. Where there is speculation I will try to put a question mark or simply use the word speculation, but I am no expert on this and it's just a brief summary of what seems to be much more complex than my pay grade:
1) Gary dies, a will is probated by his wife Gail Gygax, the estate goes to her (there is a family trust involved, but those details are too in the weeds for this review).
2) A second will is located. The kids of Gary are made aware of it, and it apparently (?) gives most or all of the estate to them instead of Gail Gygax. For a variety of reasons the kids of Gary don't want to pursue this at the time of discovery. Speculation - they just don't want to make waves.
3) Some of the kids of Gary and Gail Gygax had a falling out at some point. Some of that falling out involved the Gygax magazine. Some good will between some of the kids and Gail Gygax is burnt during that time.
4) A Hollywood producer wants to develop something from the Intellectual Property of the estate. But he wants it to be done with both Gail Gygax (his wife) and Luke Gygax (one of his sons) as co-owners of the IP? Gail apparently refuses due to a falling out she's had with Luke? Speculation - the producer was asking to include Luke because he was made aware of a possible later will and felt his IP rights would not be secure if they didn't jointly agree.
5) The producer sues Gail Gygax over the agreement they had of some sort. But, suddenly he drops the lawsuit recently. Speculation enters - did he drop the lawsuit because he decided even if he won the lawsuit, the second will could be found valid and he'd have won nothing because Gail wouldn't be the owner of the IP he's suing over anyway?
6) GaryCon, which generates revenue for the kids of Gygax every year, was canceled due to Covid-19. It takes place online this year, but there is obviously some level of revenue hit from this. The day GaryCon was supposed to happen this year, is the same day this lawsuit/probate claim was filed by Luke to decide on the new will.
7) Speculation from Tenkar's Tavern - between the double wammies of the producer wanting to produce material from the IP with a kid of Gary's (Luke) and not being able to without a will being decided in the favor of the kids, and the cancellation of GaryCon which was going to bring in revenue for the kids of Gary, the kids of Gary decided it was finally time to adjudicate the second will to resolve these outstanding issues which had such imminent financial implications for them.
Those are the supposed reasons for why now.