On forum.fregamedev.net people discuss about the decline of FOSS game development at the moment: https://forum.freegamedev.net/viewtopic.php?f=46&p=76594&sid=88c51860a7570bef8686d2ea70ad7225#p76594
I belive that there is not only a decline of FOSS game development but a decline of amateur game development in genneral.
There seem to be many reasons for that effect. Most of all I think its about the indie boom that brougth tons of cheap games to us and about the internet changed in general since 2000. People are just over saturated today.