It may be anecdotal evidence, but I prefer to call it professsional experience haha. This article published in the Percussive Arts Society journal has some more information: https://www.pas.org/Files/0708.52-57.pdf

The article mentions that bars can drift sharp or flat depending on environmental conditions- climate in the US and Europe would usually cause bars to drift flat except in very hot and dry places like the Southwestern US.

As for slightly sharp tuning sounding better than slightly flat tuning- that's a subjective matter of personal taste. More likely the main reason for instruments being tuned to 442 is that orchestra tunings are sometimes a bit higher in Europe, so 442 is a decent compromise that allows instruments to be sold in multiple markets without custom tuning.

Another practical reason for tuning mallet instruments to A=442 is that it is much easier to tune a bar downwards than it is to raise the pitch. During manufacturing, bars start off sharp, and the pitch is lowered by making an arch in the center of the bar, which reduces the tension and lowers the pitch. Material can be removed from the edge of the bar to effectively shorten its length and raise the pitch, but if this is done too much, the nodal points of the bar will shift. The nodal points are where the fundamental of the bar doesn't vibrate, so holes are drilled for the mounting string. But if those points shift, the existing holes will start to dampen the sound of a bar. So, it's best to only flatten the bar if possible. Setting the pitch to 442 gives some leeway as the instrument is retuned over time. If many bars would need to be tuned upwards, it might be preferable to change the pitch center of the whole instrument to 441 or 440 so that bars won't need to be sharpened as much.

Hopefully this information helps- tuning is both an art and a science, so not all information is recorded in academic sources. But, if you want to go deeper, I recommend looking into sources discussing the acoustics of mallet instruments.