Ain't that the truth. By the time the custom pages were implemented, and certainly by the time the new hook system was introduced, vB5 was completely dead as far as 3rd party development was concerned. You won't need both hands to count the amount of new vB5 addons released recently on vB.org, I believe.[...] and they finally did a bit of work on plugins (useful, but sadly, far too late). [...]
They just couldn't expect developers to sit around browning their thumbs for several years. Speaking for myself, I'm sure as mustard not in a hurry to update any of our products to take advantage of the new addon features, when I could be focusing on superior platforms (vB3, vB4, XF1, XF2).
All our vB5 products have warnings in red that equate to "the product is sold as-is", and any compatibility updates for new vB5 versions are applied to the old versions rather than releasing new versions.
Every email we receive where someone is interested in starting a new forum, or upgrading to vB5, I tell them to steer clear unless they are happy to run a vanilla site. I also tell them that if they are interested in a more mobile-friendly, modern forum to look at XF.
It's really sad actually, vBulletin introduced me to the world of programming, I wouldn't be where I am today without vB.