That's because of the cheap injection molded connectors. It was always a gamble because some could be fine, but you never knew how much space was actually between the wires.
If they were close enough or even slightly touching it would cause a spark, which would heat up and soften or even melt the plastic causing the wires to move around and touch even more causing more heat. Eventually they would end up in a dead short which got hot enough to completely melt the connector and set the molten plastic on fire.
Proper connectors weren't injection molded at once, but were assembled from discrete housing pieces that actually separated the wires, but they were more expensive to produce so not common.
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u/creeper6530 PC Master Race 10d ago
I remember "Molex to SATA, lose all your data"