The Confusion Of Riya
Islam is simple in practice, it is some human dispositions that take things too deeply. To some leaving a voluntary act of worship for someone is giving priority to someone else other than God is a kind of giving preference of God to someone else, that is why they call it shirk. This is subjective. Optional acts are optional because they can be left if one needs to. To have fun, too, is a blessing of God. One feels grateful after having fun. So either way, it is good for a Muslim.