There are logistical reasons why a burial may not be able to take place the same day that are out of control of the family/funeral director.
In some place the Funeral Director needs an official Death Certificate before the interment can occur. Local city and town halls don’t issue them after 4 or 4:30PM.
As was mentioned already there may be a delay from the society in approving the burial and notifying the cemetery that it is ok to bury the mais.
The deceased may owe money to the synagogue who owns the cemetery and they won’t allow an interment until the bill is paid in full.
Here, OOT, there is generally only one Jewish Funeral home in each city. Sometimes they have more funerals than they can handle in a day and try to push them off.
There are synagogues where the rabbi’s contract says that only he may officiate at a burial in the synagogue’s cemetery. If he is not available the burial can also be delayed.
Lastly, and often the most important factor is weather. My mother A”H died at about 2 AM in a nursing facility. It was blizzard like weather. The funeral home could not retrieve her body until 4PM due to road conditions. The cemetery roads were not plowed until 2 PM the next day so the interment was 3:30 that afternoon.