I've killed dozens of big game animals with Hot-Cors from 6mm to .338, and sent a bunch of small varmints skyward with TNT's.
But in general Speer hasn't kept up with the modern handloading market, and in some ways has gone backwards:
While Hot-Cors are adequately accurate, they've never been known for super-accuracy like some other big game bullets. Plus, the ballistic coefficients don't compete with some other bullets. This doesn't really mean anything in normal hunting, but somehow even normal hunters have become BC obsessed these days.
As somebody already mentioned, the Grand Slams have been turned into what are essentially heavy-jacketed Hot-Cors with an even worse BC. They don't work as well as the older GS's when they hit stuff, and they don't fly very flat. Essentially they're expensive Mag-Tips.
The Speer boattails (which do have somewhat higher BC's) AREN'T Hot-Cors. Instead they're formed like most other cup-and-core bullets, by swaging a cold core inside a jacket, and the core is pretty soft. Consequently they don't hold up on game like the Hot-Cors, though they can be very accurate. But they also don't have the trendy plastic tips beloved by hunters who tend to shoot at longer ranges.
Speer's marketing of DeepCurl bullets was inept, and then the bullets were dropped entirely, while some of the long-selling Hot-Cors were dropped.
None of their varmint bullets have plastic tips, which DO make a difference in both violent expansion and downrange performance in smaller bullets. Their really explosive varmint bullet, the TNT, has such a large hollow-point that it slows down even quicker than soft-points, and far quicker than plastic-tips, so drifts in the wind more. It is "affordable," but plastic-tips have become more affordable in recent years.
Yeah, Speer bullets work, but big game hunters who just want a reliable cup-and-core bullet often choose a Hornady Interlock instead. Hunters who want something that flies flatter and drifts less in the wind buy some sort of plastic-tip, whether for varmints or big game. Hunters who want a premium bullet can't find a real one in Speer's line.
It ain't a mystery.
