Additional features were incorporated to deal specifically with the difficulties of recording on slow-speed consumer tape formats. Increased Noise-Reduction Bandwidth Cassette tape gives a noise spectrum, without Noise Reduction, which appears to be concentrated in the high frequencies. That's why we refer to hiss rather than roar or rumble.
Noise is less noticeable when no one part of the audible spectrum is apparently dominant.
At the other extreme, noise with a distinct pitch, due to dominant energy in a narrow region of the spectrum, is especially irritating. Listening to tape hiss with B-type noise reduction reveals that the noise is not only lower in level, but that it sounds more evenly balanced across the frequency spectrum, because the concentrated noise at high frequencies has been reduced. If you were to reduce the high frequency noise by twice as much in the region of the spectrum where B-type noise reduction operates, middle frequencies would dominate in the resultant noise, and you might well describe it as a roar rather than a hiss. What you hear is an overall reduction of noise. The remaining noise is not noticeable because it appears to be spread evenly over the frequency range.