Not sure Rojas was injury prone either (or is now) - it was just one big bad injury that really hit him at a bad time (a bit like Thomas at PSV)
Yeah it's possibly just the one big injury at a really bad time. IIRC at the time he was training with the first team and starting (and scoring) during pre-season friendlies.
Yep. A lot of 'making it in Europe' is dependent on luck as well as skill - being in the right place at the right time (i.e. someone gets injured a position needs to be filled), having the right coach and staying fit etc.
It's why I hesitate to say Rojas or anyone else 'failed'. If youre picked up in the first place and continue to make a career out of it you're already way past most.