We do not write off large numbers of Jews.
In business, assets that are no longer useful need to be written off to have an accurate picture of the business financials.
We cannot do this with our fellow Jews.
Teshuvah is always possible, and if not in the present generation,then in future generations.
Just like those in Egypt who maintained their national identity even if they sunk into idolatry were redeemed, so Jews nowadays even if completely secular but they keep a national identity and marry other Jews can be part of the full final redemption.