Why are so few cancer cures recognized at Lourdes?

Because the criteria are demanding in ways that a modern cancer case almost never meets.

The criteria used are traditionally attributed to Cardinal Prospero Lambertini, later Pope Benedict XIV. Among other things, they require that the illness was serious with a poor outlook and was documented with objective medical evidence; that there was no treatment to which the recovery could be attributed; that the recovery was sudden, immediate, and without convalescence; that there was a return of all vital functions rather than a reduction in symptoms; and that the result was lasting rather than a remission.

Read that against oncology in 2026. Almost every cancer patient is receiving treatment, which alone rules the case out under the criterion about attribution. Cancers can also regress and later return, which runs into the requirement that the cure be lasting rather than a remission. And "sudden and immediate" describes very little of how cancer behaves or how it is treated.

This is a feature of the criteria rather than an accident. The process is designed to be difficult to satisfy.

Nothing in Catholic teaching presents pilgrimage as an alternative to medical care, and the shrine's own process assumes that people are under the care of doctors.