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My theory: Not everyone can solder correctly. It's much easier to train most anyone to crimp.
There is a bit more to it than that. Copper wire, especially stranded wire, is manufactured to a certain flexibility. This is done through controlled heating and cooling. In the case of annealed copper, it is so flexible that a cable as thick as a bbq hot dog could be used for jump rope. When you solder any joint, the wire is heated at that point and loses its flexibility. The conductor just at the edge of the solder becomes brittle. It is not unlike steel that is hardened by heating and quenching If this wire is in an environment where there is vibration, over time this wire is likely to break at this point. Another reason is the integrity of the connection if the wire is exposed to a short circuit condition. The inside of a fuse is basically a piece of solder. If the fuse blows, there is potential for the solder joint to also melt and become compromised. The electrical code in most jurisdictions I have seen disallows soldering only as a means of connection for this reason.
I'm an electrical repairman at a General Motors plant. No soldering allowed, we only use GM approved heat shrink crimp/butt connectors.
Those are a world apart from the average butt splices you see in the auto parts store. I'd bet the crimp tool is specifically designed for the splice used and of course heat shrinking the splice creates a weather tight seal.
In contrast someone using a cheap splice and crimpers will likely damage strands and leave it open to corrosion.
There is a bit more to it than that. Copper wire, especially stranded wire, is manufactured to a certain flexibility. This is done through controlled heating and cooling. In the case of annealed copper, it is so flexible that a cable as thick as a bbq hot dog could be used for jump rope. When you solder any joint, the wire is heated at that point and loses its flexibility. The conductor just at the edge of the solder becomes brittle. It is not unlike steel that is hardened by heating and quenching If this wire is in an environment where there is vibration, over time this wire is likely to break at this point. Another reason is the integrity of the connection if the wire is exposed to a short circuit condition. The inside of a fuse is basically a piece of solder. If the fuse blows, there is potential for the solder joint to also melt and become compromised. The electrical code in most jurisdictions I have seen disallows soldering only as a means of connection for this reason.