Why make traps if a wizard can send his familiar in to discover any? Careful players are rewarded in D&D and always have been.
While careful play is rewarded in D&D, there are also many instances of things that players are not supposed to detect beforehand. There are numerous monsters that have the "while motionless, is indistinguishable from [inanimate object]" ability.
Cursed items are also usually more impactful than traps. Traps are usually meant to sap resources in a dungeon and careful players are rewarded with less-sapped resources. And because traps are very common, it's more fine if players can completely avoid any individual trap. Curses are usually more rare, powerful, and ~permanent, and thus are more similar to plot hooks (leading to a
quest to get rid of the curse). If players could detect curses with a 1st level spell that doesn't even use a spell slot when cast as a ritual, then that'd be way too powerful. Especially since players pretty much always cast identify on loot if they have access to identify.
Also, your example would probably work for a cursed object. The wizard could have his familiar attune to it. So extreme careful play is still being rewarded, but the cost is greater (short rest to attune + temporary loss of familiar + 1 hour to resummon familiar vs 10 minute identify) In fact, I'd probably rule that the curse affects any familiar you summoned, not just the specific one that put the item on.
