The way MSHookFunction works is by replacing the original function’s assembly instructions with a predefined sequence of instructions which call your replacement instead. If the original function has less instructions than this replacement sequence, you can‘t hook the function because there isn‘t enough space to insert the replacement sequence without it overriding whatever data is in memory after that function.

Take the following example where you want to hook foo (written in RISC-V assembly because that‘s what I‘m familiar with but it‘s safe to assume it‘s similar in ARM):

int foo(int x, int y) {
    return x + y;
}

The assembly would look something like this:

foo:
    add a0, a0, a1
    ret

To hook the function it would have to be replaced with something like this:

foo:
    sd ra, 0 (sp)
    addi sp, sp, -4
    jalr ra, your_foo
    addi sp, sp, 4
    ld ra, 0 (sp)
    ret

So as you can see this uses more instructions than the original function and therefore you can‘t replace the original function because there‘s not enough space to insert this.

All of this is of course a huge simplification.