I think one element of writing ASM by hand is the programmer subliminally changes the algorithm to be 'simpler' to write.

In Java, that might involve adding more classes and abstractions to make things conceptually simpler. In C, that might involve using structs to keep relevant data together. In C++, it might involve using a std::set to keep a list of 3 constants, Etc.

It turns out that when you have to write the asm by hand and you see that double pointer dereference is a pain, you avoid data structures with double dereferences (as C data structures often end up with). You avoid classes and abstractions (as are common in Java), because they involve a lot of boilerplate. You use compile time constants for that set of three things rather than any complex hashing that C++ would do, etc.

There are lots of small things like this, and it turns out the effect adds up significantly.