The object file is in binary code, and the machine understands the binary language. So why object files are not executed?

Object files are files that are converted by the compiler. These object files can be stored for future execution purposes on another machine or the same platform. However, there are no linkings done yet to these object files. After linking them from libraries, they are converted into executable exe files.
Also, it links only those library files that are relevant to a particular platform.
Hence object codes are not executables.
Best luck..!

The computer can understand only binary language, which is object code. In your code, let's say you have used some functions like print, loops like (for, while etc.), conditions like if, case etc.
For ex: X =20
10 = Y
print(X,Y)
Compiler flags error for 10 = Y as it is syntax(grammar) error. You need to rectify the error.
In the above code, you have used print.
But how do computers know what to do with print? It does not. These pre-written built-in functions are already written in a binary language and are stored in Libraries. That means you need not write code for these functions. All that you need to do is, use them. When your source code is converted into object code, the compiler will check for syntax, if fine, converts them to object code.
and then your object code is linked with Libraries (means semantics is established)
E.g., Ravana Killed Rama. This is syntactically right but semantically (meaning implied by the sentence is "Meaningless sentence").
Rama killed Ravana is syntactically and semantically CORRECT.
In the same way, when you use print in your code, the meaning or what to do will be implied during linking to libraries. Then only object code will be converted into complete Executable code.
The Executable code, without regard for device/OS, can execute anywhere.

Object Code is verified and syntactically correct code which is ready to be executed. However, the code has to be linked with the library functions used in the program for execution. Finally, all the modules are loaded after that object code is converted to the exe file, which gets executed to produce the output.

The computer can understand only binary language, which is object code. In your code, let's say you have used some functions like print, loops like (for, while etc.), conditions like if, case etc.
For ex: X =20
10 = Y
print(X,Y)
Compiler flags error for 10 = Y as it is syntax(grammar) error. You need to rectify the error.
In the above code, you have used print.
But how do computers know what to do with print? It does not. These pre-written built-in functions are already written in a binary language and are stored in Libraries. That means you need not write code for these functions. All that you need to do is, use them. When your source code is converted into object code, the compiler will check for syntax, if fine, converts them to object code.
and then your object code is linked with Libraries (means semantics is established)
E.g., Ravana Killed Rama. This is syntactically right but semantically (meaning implied by the sentence is "Meaningless sentence").
Rama killed Ravana is syntactically and semantically CORRECT.
In the same way, when you use print in your code, the meaning or what to do will be implied during linking to libraries. Then only object code will be converted into complete Executable code.
The Executable code, without regard for device/OS, can execute anywhere.

Object files are the output of a compiler; they are binary machine-readable bits of programs that are not capable of being run because no libraries have been used at this time. There are no logical connections that the system can make and the only function that exists is the one described in the source file.
An executable has all dependencies and library files resolved and so can be executed directly by the CPU.