They're among the most successful retail operations in the world, and are a desirable employer for people working retail. Is there a specific reason you think they should "pour more time into making employees happy", or are you just inclined to say this about any company?
There was a thing a while back about Apple's retail employees complaining about low wages and few benefits, but I don't think that the allegations were ever confirmed, or that anything came out of it. The GP may have been referencing that.
Actually, a bit of Googling shows that this is still going on, with employees trying to unionize. According to [1], one person wants "to form a union to fight for better wages and benefits and to address what he says are unfair practices".
It's one guy, who says he's gotten little public support. But even if he had a deep wellspring of support: this is supply and demand. Apple is a highly specialized retailer that nonetheless can draw on hundreds of thousands of potentially qualified candidates. How could a union change that dynamic?