A very strange question.
At any rate, the answer is because (in the case of Safale-05 [and perhaps PacMan, too], for example) the yeast exhibits some interesting characteristics fermented at near lager temps. I've posted about this over the past few weeks, but Safale-05 has (for me, at least) far more interesting esters at the 55-60F range than the 67F+ range. Most posters here seem to think that this is too low and the yeast won't work. But it does work -- and it works incredibly well. Is it slower? Yeah -- fermentation takes about 24-48+ hours to get started. Safale-05 is a monster at cool temps -- incredible attenutation and great peach/tropical flavors that complement nearly everything I've used it for (stouts, black IPAs, brown ales, pale ales).
My new method is to 5-6 days @ 55-58F, and then 60-64F for the rest of the fermentation. I never secondary and leave everything in the primary for at least 21 days -- but sometimes as long as a month or a month and a half. It's slow to start, but I've had zero problems with attentuation. I'm guessing I could go even lower to start -- maybe 52F. I do give it extra O2 -- I blast it for about 3 mins initially and then another 2 mins after 12 hours. I know these temps stress the yeast, and I found that my initial batches -- without the double dose of O2 -- have definite signs of yeast stress -- weird, off-flavors and a sweet fruitiness that does not go away no matter how long in the bottle. But the O2 blasts seemed to help with the stress and what I end up with now is a definite -- but nicely understated -- peach/mango/apricot flavor that's there but not overwhelming at all.
I've spent the past six months working with Safale-05 nearly exclusively, and with the exception of some specialized beers -- hefes, belgians, kolsch -- it gives far more *interesting* flavors at cool temps. I'm doing a pumpkin ale right now -- amber ale w/real pumpkin -- and I've been fermenting it for the past week at 55F. The smell is incredible -- pumpkin pie with a definite tropical edge. I don't know what it's going to taste like -- I mashed at 155F -- but I'm hoping for something very desert-like and intense.
So we'll see.
Give cool ale fermentation a try and see what happens. You'll be mighty surprised -- especially with 05. I know PacMan is a variation of 05, so I suspect PacMan might be even more interesting. It's not some "newbie" thing. It's definitely interesting, and the results are unusual enough -- and tasty enough -- to surprise nearly everyone.