its rated on 1 pin, (generally a center pin) sometimes with a plane to sink heat, sometimes not, all to inflate the ratings above a line in the sand they have been asked to meet while meeting other engineering requirements, e.g. amount of material, density, ease of connection.
In short the reason is marketing, if they can say it meets 0.5A max per pin under this list of very specific requirements, It gets found by more engineers than saying it can handle 0.2A on every pin up to 200 cycles, with minimal trace thickness.
sometimes, like in that datasheet (marketing fluff sheet) you have to dig elsewhere to find the actual info, like what conditions the rating was tested under, what the thermal resistance of a given pin is likely to be, and from there calculate what plane areas, and what approaches you need to take to meet your spec,
Rather than them being honest, and just choosing the next pin pitch up on the listing...