An airline only has a limited number of vacancies. At this end of the market those vacancies are going to be very limited. Competition is therefore going to be intense. There is plenty of competition.
Whilst anybody can fail an exam, it is worth remembering that (however you studied the subject) getting over 25% of the entire question paper wrong in a multi-choice paper, doesn't really highlight that the requisite level of study was applied. Doing that four times, most certainly doesn't.
An airline is going to give successful applicants one "crack" at this. Obviously it wants people who are likely to succeed, and have a demonstrated aptitude for this.
Mediocre and bare minimum simply will not do at this level. There are very very few airline opportunities for low hour pilots in any event. As has already been mooted, the best course of action is to seek out career advancement jobs (wherever they might be found) and use the intervening years to show a level of application, attainment and commitment that dilutes this early lack of success.
Airline flying for low hour ab-initio pilots is an extremely steep learning curve. Where it occurs, it tends to involve a full time properly structured, managed and mentored training programme, that in itself dovetails into that airlines own training regime. This is a point that seems lost on many would be hopefulls. The belief that a commercial pilots licence and instrument rating is all that is required, is erroneous. There is a big gap inbetween that is usually only bridged by those who picked the relevant training programmes. or those who have filled the experience requirements to move on to the next qualifying stage.