Conclusion: Free ibuprofen, flurbiprofen, and indomethacin rapidly cross the BBB, with ibuprofen exhibiting a saturable component of transport. Plasma protein binding limits brain NSAID uptake by reducing the free fraction of NSAID in the circulation. https://link.springer.com/article/10.1007/s11095-006-9905-5

The article says in the real world NSAIDs, free ibuprofen, are bounded to plasma which limits the concentration that can actually cross the BBB.