They probably can judge based on past sales of that "type" of item what kind of demand they can expect and how to budget accordingly.
This is why lines can be dropped so unceremoniously as well, like Sideshow abandoning 1/6 LotR before releasing Gimli, Merry, Pippin, etc.
I don't have a problem with no removable helm on Juggs, I personally didn't care for the head sculpt on the ML one and if I had ever tracked it down would likely have never removed it.
I did have a pretty cool older Toy Biz Juggernaut that although kinda ridiculously proportioned, I liked quite a bit at the time, and had fun with his removable helmet.
Also, I do think it's fitting that ML has moved more towards making characters that will still be compatible with ML collections and won't be too noticeably oversized, like Juggy, Abom, Hulk, and so on.
HEROIC MASTER OF SLEEP