ويستحق اللائمة بتركها، إلا أن يتركها بعذر
One may deserve reproach for abandoning it, unless there is an excuse.
This statement is most appropriately understood in relation to an emphasized Sunnah for which regular observance is expected. It should not be extended automatically to every recommended or non-emphasized act, as though all occasional omissions carried the same blame.
An excuse is a legally relevant reason that changes how an omission is evaluated. Deliberate, habitual disregard is not the same as inability to perform a practice because of a recognized constraint.