Why, because they suck. People have switched to "smaller" better cams and made more power. In some cases a LOT more power, like say switching from BC 280's to Kelford 272's...the advertised degree is less but there gaining a LOT of power. Cause theres more to a cam than the advertised degree...a lot more actually. Do some reading on the subject and you will see for the older 4G63 like ours (and the early evo's) theres really only 3-4 manufactures that really make nice cams, and BC is not one of them lol. Affordable...yea, and in this case you get what you pay for too.
Manufactures I would consider buying cams from.
If I was on a budget...maybe the DKS re-grinds as even THERE better than the BCs. Only thing to really note is that with the Kelfords and some of the GSC's or FP variations of cams, you can't just throw them in and go, you HAVE to upgrade your valve springs etc. Otherwise due to the high ramp rates, your valves wont like you...or the engines pistons. (valve float)
You really should spend a LOT of time researching cams, as there a major part of your engine that decides how the whole engine responds and where it makes it's power. I for instance am planning on a set of GSC 1 cams, there a pretty good drop in cam, and there in the middle from say a HKS 264 and 272 @ 268* and still have good ramp rates etc....Far as quality goes no one beats HKS IMO. But they are dated and don't produce the most power since there ramp rates are much less aggressive. Which DOES mean less stress on the valve train. So it's not always a bad thing.