That list was made in a time where no one knew exactly which direction Bukkit/Spigot would go, and it has been so long. Many of the developers probably have left Minecraft development completely, and others are now content with staying on Spigot. Luckily a few have continued development of their plugins on both platforms, but I believe for the most part, porting old and creating new plugins will be in our own hands. As time goes on though hopefully we will see more developers bringing their plugins over to Sponge, and I believe with the version bump coming with 1.9 along with the release of 1.8.9 modpacks we will see an influx in membership in the community.
The only plugins I have so far seen ported or in the process of being ported are: