Why would I use triangular solder jumper pads?
For the same height of pad, the angled ones provide a higher length of the gap, meaning simply that there's a higher chance to find a random spot where the solder creates an initial bridge, before surface tensions "pulls" the solder to connect across almost the full height.

Also, but this is more speculation than the previous sentence, the concave  part might lead to a solder blob is centered at the "dent", minimizing the gap distance, further increasing likelihood of a successful solder bridging.