All those parts can be bought essentially off the shelf. It’s obviously not anyone can do it, but certainly the barrier to entry has been significantly lowered.
Which parts do I choose? How do I assemble them? How do I make sure they all fit together? Plus as another commenter pointed out, I can buy an off-the-shelf combustion engine. So by your logic, it should be just as easy to build an ICE car. Yet neither is easy to design/build.