The original Windows API was developed in 1984-85, over 25 years ago. Hungarian notation was a complete rage, so including a variable type in a declaration was a thing. For example, in pure C, there is no way to specify a "far" pointer, which indicates LP in LPCSTR, but in 1985 it was very important to distinguish between regular pointers and long pointers. (This value faded into the background when 32-bit windows occupied in the mid-90s, but the syntax is preserved ...)
In addition, C does not really distinguish between just a pointer to a char and a pointer to a static string. So the types are lpsz.
, , , C, 1984 . WinMain, , Windows . , , , main(), , WinMain (.. ).