I don't know if this is why you were downvoted, but please avoid using the term Welch. It's an ethnic slur against Welsh people.
> Etymologists can find no firm evidence that the verb welsh, meaning "to swindle a person by not paying a debt" or "to fail to fulfill an obligation," is derived from Welsh, the people of Wales."
Besides, Occam's razor applies. The term was coined in England, which is adjacent to Wales and historically has a degree of anti Wales sentiment.
Where are any alternative etymologies? There are none.