Even so, it still makes invisible things absurdly easy to spot. And of course there are plenty of actions that are not particularly noisy that one could easily be undertaking while being invisible that certainly should not result being auto detected.Um, someone sitting in the middle of a field invisible and not moving is describing someone who took the hide action.
If a monster, that is just assumed. If a PC, the player describes what the PC is doing, and the DM says "that is the hide action" and tells the player to roll stealth.
(The player describes what the character is doing, the DM provides the mechanics)
The case where you are invisible and not hidden basically requires you to be frantically doing something besides trying to be not spotted every 5 seconds from the moment you where invisible and the enemy knew where you are, to the current time (moving, attacking, sprinting at top speed, casting a spell, messing with your gear, drinking a potion, whatever).
Also, was blinded condition already mentioned? "A blinded creature can’t see and automatically fails any ability check that requires sight. Attack rolls against the creature have advantage, and the creature’s Attack rolls have disadvantage." Isn't a person trying to detect an invisible thing effectively blinded for purposes of seeing that thing? I would also like to point out that 'can't see' is mentioned and certainly is meant to have further implications than merely the ones specifically mentioned.