Because it's significantly easier to play alternate styles of campaign with earlier editions with no house rules.
Lol! That's funny, because it's the exact opposite of what's true.
Classic D&D was barely playable, /at all/, without house rules (even if those house rules consisted of little more than informally ignoring all the bits that didn't make sense). D&D's long dependence on the Vancian model made it worthless for emulating the vast majority of fantasy fiction, and all myth/legend. It's dependence on the cleric for healing also dictated a very specific playstyle. The range of characters playable was stunted by oddball armor/weapon proscriptions and hard-coded class-exclusive restrictions on fairly common adventuring tasks like spotting a tripwire or tracking a band of orc raiders through the wilderness.
That said, it was very easy to play classic D&D in a lot of styles and with wildly different characters and settings
with extensive house rules, because the community back then was very accepting of house rules - 'variants' as I recall them being called. House rules and DM snap decisions were the norm, so there was little to no resistance to them from players. 3e (abetted by the internet) changed all that, and the RAW became sacred, and what you could do with D&D, itself, contracted greatly (though, at the same time the d20 OGL opened up the core system to a much wider range of things beyond D&D).
In 2e and 3e there's non-combat benefits to levelling via the skill system and in all prior editions spellcasters can memorize and cast non-offensive spells.
And, in 4e, there's a skill system where leveling /really/ maters (unlike 2e's proficiencies and 3e's ranks where you needed to pour proficiencies or ranks into a skill just to remain OK for your level, while all your other skills became increasingly worthless). And casters don't need to memorize non-offensive spells, they get utilities automatically, and can learn and cast rituals without having to trade-out combat spells. That made the game much better at doing /both/ combat and non-combat.
4e was purposely designed around the "sweet spot". By its very design goals it is a more narrow play experience.
The 'sweet spot' in question was the narrow range of levels at which prior eds of D&D tended to have some semblance of class balance and had the best chance of being fun for everyone at the table. It's not a narrow range of play styles, it's a narrow range of levels /at which the game worked/. In earlier eds, the game worked at levels from 4-7 or even 2-10 or so, but was always a pain at 1st and fell apart by the teens. 4e worked from 1-30, an unprecedentedly broader range of levels than ever before.
It also worked with a much broader variety of play styles, since you could alter campaign pacing without wrecking class balance, and could use a more varied mix of archetypes without trashing party effectiveness - most particularly and obviously by having leaders (healers) of varied archetypes (sources) and moving daily healing resource from the healer to the character being healed. It also gave the most sophisticated out-of-combat challenge design and resolution system to date (sadly broken though it's first iteration indisputably was).
5e is supposed to try to take the best from all editions, and 4e has a lot of 'bests' to contribute. Miss-characterization of the positive aspects of 4e only does the development of 5e a grave dis-service. The edition war is over, 4e is dead, but there are still a lot of goodies to be looted from it's body.
