Is Swift loosing adoption ?

No, Swift isn't like other langugaes which start from nothing. Most languages come out quietly and build a userbase slowly but steadily, which results in more organic growth, so they will have a steadier curve. Existing developers however have no real pressure to move to the new language, and can do so at a comfortable pace IF they decide it is even worth learning.

Swift however was released to a huge population of existing iOS and Mac developers, in releasing Swift Apple basically set a timer on the end of life of Object C and it meant that all developers at some point or another HAVE to learn swift to continue having a healthy career as iOS/Mac developers or be relegated to maintaining legacy code (which usually doesnt last long for client applications). So they release it, instant exposure to all existing Objective C programmers, instant interest from nearly everyone in their target audience (existing developers), and they're all in a rush to begin learning about it as staying relevant depends on it. However once a large subset of existing developers have already learnt about it, interest dies down again and it evens out at a rate you would expect from any other language based on interest from NEW developers.