They send troops to fight the horde, honoring their debt, which were initially not even wanted by Lothar, because he was afraid the elves would take leadership. later they sent their main army to assist to defend Lordaeron after it became clear the horde was a real threat, after the second war the human kingdoms distanced themselves from the non humans in the Alliance and Lordaeron decided to imprison the orcs and wanted money from all the Alliance nations which is the main reason the Alliance broke apart.
The high elves retained ties with dalaran and their crown prince served in that city as such the Alliance and they send priests to investigate what was going on. Bottom line is the elves owed the humans nothing and vice versa.
Heck high elves did more for Lordaeron during the third war then Kul tiras, Stormwind, Stromgarde and Gilneas.