This could be their way of allowing more conductors on the same output, for lower resistance at higher currents. This is also common on the power input side of some really big amps, they'll use multiple 1awg connectors. Some of the higher wattage speakers have multiple voice coils, typically 2, so this would also be a convenient way to give each voice coil it's own set of wires.

One thing to keep in mind, especially with the older amplifiers, is car audio competitions is a thing and manufacturers use it to sell amplifiers (and other equipment). Cars are grouped by power classes. The power at a specific ohm load. i.e. one class for up to 100w at 4-ohm, one for 200w at 4-ohm, etc.. so then it became very popular for car audio amps to put out some smaller power number at 4-ohm, but enormous amounts into very low impedances, some stable down to 1/4 ohm. This way they could compete in say the 100w class, but actually have 1000w+ available. Anyway, audio amplifiers are neat and this guy tests a bunch for anyone who is interested:

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Many of the better amplifiers are rated for their output at some very low distortion level, while most of the "junk class" amplifiers are rated for power output at 10% harmonic distortion.
And then there is also the "IHF" power output rating, which is the power output into a perfect load, with a perfect power supply substituted, and for one cycle. Some folks may recall that rating scheme that was used by some for a while.

But what sort of program material would be played at that level to a willing audience??? I do recall a vehicle that visited somebody down the street, whose sound system material could be heard for several blocks before they arrived, and that was certainly some noise. It was much worse than the kid with Lake Pipes racing his engine in front of that house at 3 AM.