Factual error: When Alex, Marty, Melman and Gloria emerge from the water at Port De Monte Carlo, the snorkels they used to breath in were under the water. They could not have been able to breath if the snorkels were in the water. (00:05:50)
Factual error: After Captain Dubois escapes from jail, she looks up missing lion on a computer and finds a news page with Alex on saying "FAMOUS CENTRAL PARK ZOO LION MISSING" and hits the Print Screen button on the computer and the news page prints. However, pushing the Print Screen button wouldn't print a document. It would just take a copy of the screen. No matter how much you push the Print Screen button, the page wouldn't print off. (00:40:20)
Factual error: During the casino scene, we see a roulette hand and the ball is landing on 36 black. In real roulette games, 36 is always red.
Answer: They don't make an appearance because they were irrelevant to the story. The decision to go back home would have been made with or without any character introduced in the previous movie, so they were simply not included. Alex's parents would have continued to live in Africa after Alex and the others left.
Casual Person
That makes no sense though because (I know it's a kids movie) but the way they portray it, it makes it seem like Alex doesn't care about leaving his parents and what he just recently realised is his birth home. Like, it feels like there was some necessary dialogue there (probably not for the kids though).