Why can't we say that an Internet browser lies in the application layer of OSI?

Internet Browser does not exactly lie in the Application Layer of the OSI model but it uses protocols which reside in Application layer. For example HTTP, DNS, SMTP, POP etc.

we cannot say so because the Internet browser is actually a tool for user to get benifitted from the protocols used at the Application layer like http,https,dns, etc

At the very top of the OSI Reference Model stack of layers, we find layer7, the application layer. Continuing the trend that we saw in layers5 and6, this one too is named very appropriately: the application layer is the one that is used by network applications. These programs are what actually implement the functions performed by users to accomplish various tasks over the network.