Why are Orthodox Christians expected to go to confession if they don't distinguish between mortal and venial sins and they don't believe in Purgatory?

I assume that the average Orthodox Christian doesn't confess every minor sin right away, but is still able to receive the Eucharist with a clear conscience. On the other hand, they would want to go to confession first if they have committed a very grave sin. Without a distinction between venial and mortal sin, though, why is confession necessary at all? Without Purgatory, it would appear especially unnecessary to confess one's more trivial sins, not to mention that Orthodox priests do not even absolve sins. On the other hand, would Catholics still be required to make regular confessions if not for their belief in Purgatory and mortal sin?