Hi @uchiha,
This may be worth a read.
Electrical resistivity is basically a measure of how effectively electrical energy being transferred through a given medium/material is converted into other forms of energy. While that can include sound, light, and movement, in the case of wires that we use as conductors it’s mostly heat.
Applying an electrical potential (voltage) over a conductor induces a flow of charged particles, which is resisted to some degree by the conductor’s physical properties. Power drop isn’t so much the cause of heat generation as a measure of how much of the input power has been converted from electrical energy into something else (by the resistance).
Ratings are determined based on all properties remaining within desired/functional limits. Current ratings on wires are generally determined based on when the insulation would get excessively hot to the point that it can harm people, or cease to be effective (e.g. burn/melt off). Accordingly if you have very thick insulation, or just materials that are heat-resistant or very thermally conductive, the rating can be quite high. The properties of the conductor itself also matter, but generally our insulation materials get damaged well before the conductors do, and the electrical characteristics of a wire tend to stay mostly unchanged while in the usable temperature range (which isn’t the case for many components).
As @hscadden mentioned, the T200 wires are quite short and mostly surrounded by cool, and often flowing, water. Given that context, the temperatures that can be reasonably expected to occur are significantly lower than the “standard” testing conditions that most ratings are provided under.