I think people say they are harder due to a few factors, worth noting is that it is in reference to purer sativas rather than the hybrids. They do take longer to flower, newer folks also might not plan correctly for the stretch. Probably variety dependent, but they are more sensitive to overfeeding, thus being easier to botch. Not really more difficult, but they do better under 11/13 or 10/14 than 12/12. Not personal info, but some sativa aficionados say they need certain light spectrums to really shine.
Idk, its worth the extra flower time and not terribly hard to adjust the other stuff for some top quality dope to smoke
I like to compare growing weed to brewing beer, some are more of a challenge to produce but its for a more exotic end product.