The way I see it, one of the reasons might be because the EOC believes the Eucharist can have an negative effect if one receives it with unworthiness. So perhaps the EOC practices a closed communion because it thinks it can have an harming effect on those who are not of the same faith, worship and ecclesiastical life ? Or is it politics? A way of making people convert to the EOC? It would also be interesting to have a grasp on the OOC concerning this.
I think this is why. I was a little jealous when I first went to an Orthodox church and realized I couldn't take Communion. If, God willing, I am one day ready to make the conversion, that will be something I can do. I have to see that they are this way for a reason. I have to humble myself. Not easy, but worth it in the end. 
What were you referring when you said "I think this is why" ?
I am an EOC (Romanian Orthodox) , and I have a hard time understanding this and also the possibility of an Orthodox layman to be banned from the Eucharist or even get Excommunicated (Expelled).
A few points.
1. Being banned from the Eucharist and being excommunicated are essentially the same thing.
2. Such actions are not restricted to the laity.
3. Excommunication is very common and is effected by members who do not partake of Holy Communion of their own volition, sinfulness or laziness. We are all called to commune, not once, four times, or monthly but each time that the Lord is offered to us for the healing of soul and body. We approach the Holy Chalice after we have repented of our sins, reconciled to our enemies and the Church, forgiven those who have wronged us, and have led the life we are called to in general: fasting, praying, etc.. in accordance with the standards of the Church. None of those make any of us worthy--even patriarchs, but when we approach Christ even though we are unworthy, we must have tried to lead the life of one of His disciples. So, when we do not take Holy Communion for reasons that are not acceptable for one of His disciples, we excommunicate ourselves. What I do not understand is the mentality of those who take communion once or four times a year. Even with greater preparation, how can the Church excuse the unpreparedness for more frequent communion, not as a matter of exception but a matter of course?
1. I used excomunication with the meaning of expelled, even though that is not quite the Orthodox term, I wrote in the parentheses EXPELLED.
2. It doesn't sound good to me for someone to be able to get unorthodox and deprived of the divine blessings in the Orthodox Church through the judgement of priests/bishops. I mean who gives them the right to lose the souls of people and deny them the heavenly gifts?
3. The worthiness card is implausible and puts God under a black spot . Why would God harm someone because he did not do well in a magical rite?
All of your points would be valid if Holy Communion was a magical rite.
There is no magic in any of our Holy Mysteries where the clergy are magicians and we are the recipients of that magic. In all of our dealings with God, we are active participants.
If you examine the Divine Liturgy, it is not a rite performed by the clergy only for the benefit of the laity, but it is common work that is performed by everybody, clergy and laity alike for the life of the world. Indeed, there are very few prayers by the celebrant that are personal in nature. Most prayers are offered by the deacon and the priest for all of us. Those prayers are not completed until everybody gives assent by saying amen, Lord have mercy, to Thee oh Lord, or grant this oh Lord. During the Epiklesis, the priest calls upon the Holy Spirit to make the wine and bread the Blood and Body of the Lord and that prayer is also not complete until consent is given (either by the people or by the deacon speaking for the people.)
Each one of us is part of the Royal Priesthood of Christ: "But you are a chosen generation, a royal priesthood, a holy nation, His own special people, that you may proclaim the praises of Him who called you out of darkness into His marvelous light; who once were not a people but are now the people of God, who had not obtained mercy but now have obtained mercy." 1 Peter 2:9-10.
So, the people of God are not mindless sheep or newborns who cannot help themselves and are thus subject to the care and mercy of the clergy. The people of God are not nominal, conditional or associate members of the Body of Christ; they are full members. A such, it is their responsibility to take care to not to separate themselves from the Body. The Church may recognize that one of the Body is no longer in communion with Her, but like the prodigal's father, She patiently and with love prays and awaits for the return of the prodigal. Accordingly, it is the hard heart of an unrepentant sinner that is responsible for any formal excommunication by the Church, which in this rare instance merely recognizes the state of affairs that was brought about by the excommunicated one.
