ContactTower,
Essentially some get jobs whilst others don't because it does boil down to your grades and performance over the course.
Since I have been in the OAA holdpool, aside from Ryanair, only two jet jobs arose - flying as an SO for Air Atlanta Icelandic at no cost to you, but only secure for 2 months, or flying as an SO for Volotea, at a cost of £25K for a B717 TR. No turbo-prop jobs have been offered unfortunately.
In my case, I did not apply for either as Air Atlanta Icelandic would have clashed with my CTC Airline Qualification Course training, and at the time, I didn't think it suitable to spend a vast sum of money (albeit on a jet) on an aircraft that had such a limited amount in service in Europe.
Sometimes people can refer to it as 'pot luck', but the blunt matter of fact is, that most graduates up until now, have qualified at OAA and then attended Ryanair assessments. Some have been successful, some haven't and unfortunately there seems to be no rhyme or reason as to their recruitment methods - so I can't comment on that unfortunately.
You need a high standard to be considered for job interview. When OAA send out an email to all graduates stating there is a job available for 'said carrier', you will be competing against perhaps 100 other individuals (it was once less, but now CAE have taken over OAA, they've added their pilots into the mix) who are just as ambitious and as driven as you - if they have better grades, reports and above all, perform better on the day - they will get the job, not you.
Aim for above 90% on your ATPLs, with no failures in those exams whatsoever, as well as first-time passes in your CPL and ideally your IR. A good MCC report is crucial too. Your CV needs to show you 'have a life outside of work' too, so make hobbies and subjects studied varied, and not just about aviation.
OAA run 'Interview Preparation Workshops' and also host seminars, I believe tomorrow is with Air Tankers on their role with the RAF.
My role is contracted out to the orange carrier, so unfortunately I do not work directly for them. But, this orange carrier is a prominent recruiter from the CTC hold pool, and prior to my graduation, operated the APPFO+ scheme to take on graduates from OAA. Although this approach may look quite like I'm adopting 'tunnel vision' in my search for a job, it can't hurt to have fingers in different pies so to speak.
The orange carrier is my dream airline, but we shall see. 'Best laid plans of mice and men often go astray'.
Good luck, you can PM me if you wish buddy.