Why didn't Harry continue Dumbledore's Army sessions in the Half-Blood Prince?

Why was there no Dumbledore's Army in the Half-Blood Prince?

In this year Snape is appointed as the new Defence Against the Dark Arts (DADA) teacher, and teaches, if my memory doesn't fault me, difficult non-verbal spells. It seems strange to me that Harry didn't recreate the DA. At first I thought he didn't want to annoy Snape, or to meet his anger, but Harry doesn't seem particularly frightened by Snape.

I just thought that, had the DA continued in Harry's sixth year, many of the former members could have greatly improved their dueling skills (as Neville did) and maybe the Battle Of Astronomy Tower could have been less bloody (Dumbledore would have died anyway).

I thought Harry didn't have the time, but thinking about that, he managed to successfully lead it in his previous year, with the OWLs, a couple of classes he eventually dropped before HBP (Care of Magical Creatures and Divination), and with the whole Voldemort-scar thing that gave him a hell of a year.

In the OoTP he didn't have the Quidditch training because he'd been banned, but in HBP he had more time he could use to tutor his friends. Maybe with several Death Eaters in Azkaban he relaxed a little, but he did know that Voldemort wasn't in prison. He almost seems to forget this.

He didn't even have to worry about being discovered, with no sneaks or Umbridge standing in his way. Maybe Dumbledore didn't want him to continue because he was afraid he could use his army to thwart Malfoy's plan? But Dumbledore had already arranged his death with Snape and had already told Harry several times not to worry about Malfoy. Harry, anyway, asked Dobby and Kreacher to keep watch on Draco.

I'm relatively new to the Harry Potter franchise, I've read the books a couple of times (I have seen the movies, but I don't particularly like them after Goblet of Fire) and I apologize if my question is stupid.