Why aren't instructions' adresses consecutive in machine code?
The first column is the address of the instruction.
Because x86_64 instructions aren't the same length (like ARM64 for example), the value difference varies. The second column show the bytes of each instructions. Notice that they have different lengths.
Each instruction can take more than one bytes of space. Here, the first instruction takes four bytes of space(f3 0f 1e fa) so the next instruction starts at byte 4.