Simply because Spike couldn't act like a proper demon and do the usual bout of torture and murder at one particular time and location, the Buffyverse was forced to endure decades of this joke (just like our own universe)...
"You want me to do what?!" blurted out a disbelieving vampire during sometime in the early part of the 20th century.
Standing in the pouring rain outside a house a few miles from a rural Pennsylvania village but near to the railroad tracks where he'd hopped off a passing train earlier tonight, Spike had his paranoia abruptly surge to record levels inside his mind. That incredible offer just made by the bewhiskered man inside the house had to be some sort of trap or plot against an invited Spike about to enter this dwelling and then promptly slaughter everyone there. Why else would the old bloke have come out with this really suspicious proposition?
Spike warily backed up from the warm, dry interior of the oil lamp-lit house where two people were gazing in mutual surprise at how oddly their latest visitor was behaving now. This pair of humans then saw how the blond man soaked to the skin took another few steps away, mud squelching under his boots, as he mistrustfully glanced around in the absolute darkness filled with a heavy cloudburst from above.
He damn well couldn't see, hear, or smell anything in this filthy weather, so it was far past time for Spike to speedily sod off before whomever was lying in wait attacked with their stake or holy water at hand. Before then, at least the vampire could have the last word.
"Nice try, but you'll have to do better than that to finish me off, gaffer! I don't know or care how you figured out who I am, but that bloody stupid invitation was just too overdone!"
With a final sneer directed at the gaping pair standing behind the open doorway, Spike whirled around and rapidly ran away out of sight.
A few moments later, the younger of the two people in the house stepped forward and she closed the door. This bewildered girl then turned to her father, plaintively asking him, "Paw, what on earth was he talking about?"
Tugging with equal perplexity at his beard, the man eventually answered his child, "I haven't the slightest idea, honey. Never mind, let's get back to our dinner."
A couple of minutes later, there came another knock on the house's front door. Tossing his napkin onto the table by his plate, the man declared with evident satisfaction in his voice, "I thought so! It took him long enough to change his mind!"
Getting up from his chair, this older male headed once more towards the door, followed along by his offspring also leaving her own familiar spot at the table. Except, when these two people opened their door to welcome whomever was there, they saw an entirely different person outside the porch in the still-drenching rain rather than the peculiar stranger also there a short while ago.
This newcomer dressed in a dripping hat and coat while carrying a small suitcase tucked under one arm blinked at the astonished looks he was getting from both the weather-beaten guy and the very pretty girl standing in their home. Clearing his throat, that outsider appealed, "Hello, folks. My car's stuck in the mud down the road. Can I stay here until morning, and make a phone call to have it towed then?"
Staring past the man in the rain, with a frown showing among the part of his face not hidden by any facial foliage, the puzzled homeowner distractedly replied, "We don't have a phone, mister. Say, did you see anyone else out there a minute ago?"
"Huh?" blankly replied the newcomer. "No, why?"
"Oh, nothing," broke in the girl while sizing up the evidently prosperous arrival. "Come on in already! Let me take your case."
At those last words, she bustled forward when the other man entered the house to then determinedly remove that same small container from the grip of their new guest. Glancing down at what she was holding, the girl delightedly squealed at reading what was lettered on the suitcase's side, "Elizabeth Arden Cosmetics!"
With a polite nod, the stranger confirmed, "Yep, ma'am, I'm in that line, going to stores to show off my samples. I'll let you look at them later, if you like."
Hearing his only child's gleeful giggle at this unexpected opportunity, the girl's father knew that it was now the perfect time to once again raise the slight difficulty regarding anyone who had to remain overnight in their small house. However, now that the ice had been broken instead of coming out with the problem right away as with the other potential guest, it seemed likely that this occasion wouldn't end so inexplicably.
Clearing his throat, the farmer informed the traveling salesman, "Young feller, you're welcome to stay the night, but since we've got only two bedrooms here, you'll have to sleep with my daughter."