Demons are a bit more nuanced than that.
Some are neutral rather than evil (being more like Japanese yokai) the only thing is that they are mostly chaotic. But some true neutrals do exist. These type of demons are highly variable from Oni like creatures to Succubi, as well as elemental beings, and anything in between, we get the joking cutesy demons in Imps and some Succubi, though other Succubi are more serious business.
Many demons are more or less just "contractors," especially neutral ones, either acting independently, or under the service of someone, a summoner/wizard, or more traditionally a Baron of Hell, which is a specific type of Lawful Evil demon.
Barons are the typical scary, no nonsense demons, but a bound by a series of codes and traditions.
Since Barons are tightly constrained to taking only lawful actions as defined by the Demon Code they resort to hiring demons to take chaotic actions on their account.
Angels are similarly constrained to being strictly lawful, and rarely you can find chaotic good reformed demons working in service of an angel. This has lead to a good cop-bad cop pair of an angel and her hired reformed succubus appearing in this setting.