Yea, it took them 3 years for Season 3 and Aaron McGruder said it was the final season literally since the first trailer "leaked":
I never totally understood the boondocksbootleg site as if it was really "bootleg" or official. They had the scoops and released the trailer, but then there was some filler stuff that could have been like a bootleg site
That trailer is all the proof you need right there.
The time length is fitting though. Took a year for season 2, took 3 for 3, and now 4 for 4 (the source being my memory).