It was long ago. High elf lord Alkarion commissioned a guild of dwarf craftsmen to construct a temple. After many months of labor they had finished what was a masterpiece of artistry and engineering. Something that would stand for the ages a testament to the guilds skills. But then time had come to collect payment?.
AND THE ELF LORD REFUSED TO PAY!!
Such an insult was unforgivable! Outraged, the dwarf king declared that for all time no dwarf would ever work for an elf again. An animosity that persists to this very day.
(on a side note the dwarfish word for elf also means deadbeat)