Excuses are what you come up with when attempting to convince about something you did (and shouldn’t have done) or did not (and should have done).
Reasons are circumstances that explain why you have not done something you should have, or have done something you should not have.
Excuses are fragile. They are usually ex-post (they come after the fact). They border with lies, and as nobody wants to think of themselves as a liar, they set up for discordance and self-criticism, and eventually undermine the intention of doing.
Reasons are solid. They are usually ex-ante (they come before the fact). They fire up compassion and kindness towards ourselves, and they do not harm our will to do what we initially set out to do. Perhaps under different circumstances, or better equipped to face the ones that have emerged.
Eventually, only you can say if it’s excuses or reasons you are using to not show up.