This answer is using the current version (1.12.651680) of Age of Mythology: Extended Edition, on steam.
It sounds like you are playtesting a scenario within the editor, or going into single player and selecting Load Scenario.
When testing a scenario in these ways, players with control set to Human will not have scores appear. However, when you load the scenario for multiplayer, all of the players will have their scores appear, regardless of how they are being controlled (AI or Human). See images below.
Note that if you want Player 1's score visible in a single player scenario, setting the control to unavailable will achieve this (And player 1 can still be controlled)
Player List in scenario editor
Players in single player (note the players who were Human are absent)
Players in Multiplayer