Why would Toyota make higher tone horns? Is it cheaper and they are saving money? Do they not have the engineering knowledge to replicate a 1970's Cadillac horn?
The real answer is probably based on physics and human physiology.
Fact 1: sound transducers, which is what a horn is, are more efficient at certain frequencies. As a general rule of thumb, if you have say 10amp wiring dedicated to a horn, a horn transducer tuned to 1000hz will be louder than a horn transducer tuned to 700hz. Lower frequencies require more energy than higher frequencies for the same output. If you are limited to 10amps, you get more sound pressure output if you go with a higher frequency.
Fact 2: Human hearing is more sensitive to higher frequencies, up to a point, when it starts to roll off. If you have two horns, one 700hz and another 1000hz, and they both produce the same sound pressure levels, the 1000hz will appear to be louder to a human ear. That's why if you have a home theater system, at full blast your sub-woofer might require a 500 watt amplifier, and your tweeter will use only 20 watts.
So, the high sounding Toyota horn is beneficial in 2 ways, it generated a higher sound pressure level, and on top of that the perceived loudness of the tone is higher also. The horn is a safety device, not a macho fashion accessory, and I would argue that a Toyota horn is much better at grabbing the attention of other drivers.