I'd say it's probably three factors working together. First is the one you mention here; in any alignment debate or "How good is Good?" discussion you'll see people conflating D&D morality with real-life morality because it's a common reference point, even though there's a big difference between the two both socially and cosmically.
Second, there's tons of Good-aligned stuff in the game (monsters, classed NPCs, items...) that rarely gets used in an antagonistic capacity because comparatively few games involve evil PCs. A group that's already seen a lot of (and gotten used to the standard flavor and tactics of) demons, devils, evil cults, and so forth can find a squadron of Pelorite paladins mounted on pegasi with some Radiant Servants of Lathander support to be a refreshing change of pace against which a lot of standard tactics and gear prove ineffective. That's probably why the Burning Hate more frequently shows up in the context of DMs wanting to throw something different into their next campaign rather than PCs wanting to play clerics of evil!Pelor.
Third, a lot of settings have Evil (or sketchy-leaning Neutral) gods among the most common pantheon(s), and authors and DMs tend to have to go to some trouble to explain why people would put up with churches of evil gods in polite society at all--Umberlee the Sea B*tch is worshiped to keep her away from shipping, Bane is all about civic order (or else!), gods of death can be worshiped as gods of "please let my dead grandpa stay dead and not spontaneously animate as an undead creature" if you squint, and so on--which also happens to make the gods feel more three-dimensional and make the setting feel more immersive since real-life gods are rarely God Of This One Particular Thing and tend to be more multifaceted. Fleshing out some Good gods and giving them closet skeletons like Zeus's dalliances, Thor's anger problems, and the like can give you more verisimilitude in the same way.
(And, as a side effect, it can help turn Neutral gods from "Why the heck would you ever fence-sit between obvious Good and obvious Evil!?" to more of "Well, the Evil gods aren't all puppy-kicking jerks and the Good gods aren't all sweetness and light, so at least the Neutral gods aren't putting a big PR spin on things," which adds yet more believability and also opens up more Neutral antagonist options.)