The Ten Virgins, including the five who were not prepared, must have (1) believed in the bridegroom, and (2) that the bridegroom was coming or they wouldn't have been waiting.
So, it seems that (1) we cannot assume eternal salvation, and (2) the un-preparedness of the five suggests they failed to run the race to the end.
Truly amazing, weddings are the same around the world; you do not need to be saved to participate in a wedding procession. The bible is silent about whether the five bridesmaids without oil were saved or not saved, when the bible is silent about an issue then we should be silent also. "Biblical Rules of Interpretation 101."
Your bias about the Bridesmaids failing to run the race to the end is because, "Eternal Salvation" is offensive to you. Your assuming that the bridesmaids lost their eternal salvation is your opinion only, the bible does not say they did, so that your interpretation and applications are false. Eternal Salvation is supported by the bible in many places.
John10:28
28I give them eternal life, and they shall never perish; no one will snatch them out of my hand.