Well, ultimately, the only things most people used those jump packs for were combining them with blood claws boxes to get cheaper ten-man assault squads. When GW priced the Assault Squad boxes at 25.00 USD apiece, it came out the same to just get two Assault Squad boxes, and you get better looking models with the jumping legs. That makes demand for the jump pack bag go down. The other thing a lot of people used the jump packs for was giving them to pewter character models (namely Chaplains) but GW made a Chaplain with Jump Pack model, so the demand for the packs, again, goes down. That just leaves people who need them for a commander or librarian, and at that point, you're probably pulling a man out of an assault squad to get a nice even number of models anyway in the squad being lead by the character, so the assumption is you take the fifth jump pack out of the assault box and use that.
I'm not defending GW pulling the bag-- I thought it was a damn useful thing, and I always wished they made just like... a bag o' random Space Marine sprues, which didn't necessarily amount to anything, but had legs and torsos and heads and random special weapons and whatnot... just generally useful bits. Or sell a box with nothing but a couple of the upgrade sprues (which they sort of did with the Black Templars, but it didn't really take, unfortunately-- I love those boxes.)