The reason for this is that /ialfill will not allow you to repeatedly refill the IAL if it is already full, ie. contains addresses of all of the nicknames on the channel.
The IAL is usually filled with nicknames and addresses when you join a channel on networks that support the IRCv3 extended-join token. If a network does not support this, the IAL will not be filled.
No other details are filled, since these are not provided by the network on a join.
If you want to update other properties in the IAL, such as .gecos, and the IAL is already full, you will need to use /ialclear and then /ialfill.
Note that if you do this too often, you may be disconnected by the server, especially on channels with large numbers of users.
Also note that .gecos, .away, and .account can change, so the IAL may not always contain the latest information. Except on networks that support the IRCv3 setname, account-notify, and away-notify events, in which case the client will receive notifications of changes to update the IAL.
Last edited by Khaled; 28/09/20 08:55 AM.