The world which the Xurkitree call home is known for its fierce thunderstorms, which shaped the evolution of these pokemon; rather than relying on its distant sun, Xurkitree obtain their energy from lightning. Beheeyem have been known to visit Xurkitree's world, which they have named the Ultra Plant, to refuel their spaceships; not only are they built to absorb lightning, but the Xurkitree's cable-like branches can themselves be hooked into Beheeyem spacecraft, allowing them to drain electricity from these pokemon. Thunderstorms on Earth, however, are less intense and never constant, so those unfortunate Xurkitree who fall through the Ultra Wormhole are inevitably extremely hungry. Had the wormhole opened even 140 years ago, any Xurkitree to fall to Earth would have surely starved.
In the present era, however, electricity is not a mysterious substance wielded by a small percentage of pokemon, but an omnipresent force that powers the whole of modern society. Xurkitree who land outside Sinnoh find ample "food" growing on power lines, complete with curiously compatible black cables, and even there, Xurkitree's root networks, unlike a Pachirisu's paws, can easily siphon away the region's electricity. Blackouts, as a rule, are lengthy when a Xurkitree visits this world; if it is not captured or driven off quickly, hundreds may die of heat stroke, food poisoning, or treatable illness as the region strives in vain to function with only electric pokemon to supply power.
If there is any reason to take solace, it is that Xurkitree are no happier to be in this world than we are to have them here. If one can communicate to their alien minds what the Ultra Wormhole represents and help them off the ground, they will gladly return home. And when they leave, the stars on their heads shine with a brilliant, beautiful light.