Dumbing down of interface in 3.0 made creation of custom filters complicated to the point of being prohibitively time-consuming.
But ability to generate custom filters on the fly was one of the main reasons to use ABP in the first place. Because filtering of hosts with ready lists can be done by simpler and thus lighter addons. Or on several other levels (all the way down to hosts file) that don't involve sticking more addons into already memory-hogging browser.
Thus it went from "indispensable" to "barely useful".