I wouldn't say 'there was no reason'. In hindsight, given how many games we lost, it wouldn't have been wrong to experiment a bit more. After we lost Rodri, I wrote that we should rely more on the younger players. So, I understand what you mean. But we wanted to stop the sequence of losses as quickly as possible because we still hoped we could fight for the title. Maybe Pep made a mistake to insist on the most experienced players. My point is that it was far from obvious that O'Reilly would have done better than Gundogan or Bernardo. He might have done better or he might not. Pep went for experience over running power. Again, in hindsight, that might have been a mistake. In real time, given our ambition to compete for the title, it was a difficult call.
There are trade-offs between playing experienced players who have won everything and know the system and playing young players who are hungry and can run but lack the experience and knowledge. You don't seem to get the trade-offs here relying too much on hindsight.