 Solution

The primary outcome addresses the main prespecified question; the secondary outcomes involve several additional comparisons. Testing each at $0.05$ would increase the chance of at least one false positive across them. The smaller secondary significance level makes their individual tests more conservative, reducing multiple testing problems.

This is a design distinction between confirmatory and additional outcomes, not a claim that secondary outcomes are intrinsically less important. A level of $0.01$ per secondary test does not by itself establish a particular bound on the familywise error rate unless the whole testing plan and number of tests are specified. Likewise, having two primary measurements still needs a clear prespecified reporting and multiplicity strategy.