You know finding good Airdrops nowadays is a herculean task, some of those websites you listed used to have or promote good Airdrops once in a while, and in the absence of Airdrops they still post relevant news so as to remain relevant still and when a good one comes up, they post it also. Now looking for a platform which posts only airdrop might be hard, because it will mean that if there is no airdrop the website or platform will be dormant in this case users might lose touch of it. So in my own opinion, just like others have suggested, make use of the altcoin section most times there are Airdrops too and also keep in touch with those websites as well should in case a good one comes up you will get the notification.