Why are avocados ballsacks of rubber when you grill them?

Seriously, I've been told recently that grilling avocado can be a great meat replacement and since it's hard to find non-soy meat alternatives where I live I tried it and it was... awful. It was super rubbery and tough and felt like biting through a pencil eraser. It smelled like old tires. What did I do wrong, if anything, and (more importantly) WHY did it turn into something so... inedible?