Lack of Resources
Currently, the registered overseas voters are about 90 Lac. However, according to the logistics viability, if only five thousand people in a day go to the consulate, it gets choked. Even then, depending on their domicile and where they used to live they can vote for certain MNA and MPA candidates as we are a parliamentary democracy and don’t vote directly for a leader. So to say they will all vote for any one party doesn’t make sense to me. There has to be a lot of printing.
The postal Ballot is the most probable issue. Voting by post is usually done before the election somewhat around a month early. Sometimes the Vote difference is less than the rejected votes. This is where the overseas votes can alter the voting results. Look, for example, in the neighboring country of India, the different state’s polls swung because they had multiple delays in voting and thus the earlier results somehow affected the convention of the winning party.