This strikes me as the biggest reason not to use the CC BY; the "virtuous circle" created by the OGL's viral nature was an excellent way of encouraging the remix culture that's part-and-parcel of RPGs. Going with a license which doesn't necessitate that (it's still an option, but it's an unfortunate truth that there are all too many people who will use open material without making what they derive from it subsequently open) strikes me as a loss for the community as a whole.
The problem is that viral licenses always help the top of the food chain. Whoever creates the original work is under no obligation to release all of their material under the license but then forces that obligation on everyone below.
WOTC never released the whole Player's Handbook under the OGL. They released a subset. But every producer below them had to release everything they produced that included material from WOTC's SRD under the OGL – which meant WOTC could theoretically use that in their own products but not vice versa.
There's a wide range of CC licenses, including CC BY SA that do require downstream producers to release their material. An updstream producer can release some of their material as CC BY SA but then any downstream producer that uses any of that material has to release all of their related material under CC BY SA. Hence, the virility.
There's another issue with the OGL which is that it's still a license owned by WOTC. That was their argument back when the OGL 1.1 happened. They argued it was their license and they could deauthorize it. They later said they wouldn't do that but not that they couldn't do that. So why would we trust the license now? Why not switch to a better one? Why not switch to one trusted by maybe millions of individuals and hundreds of big companies – one that's been used and refined for almost 25 years?
Anyway, people can do what they want, but that's why I focus on using CC BY. I don't want to lock in downstream producers and one more widely used and trusted across the whole world.