>>4579862Ebonheart Pact actually makes sense when you delve into it. At a surface level it's the least likely Alliance, sure, but they do go into that in the game, the tension there, etc.
It all comes down to the fact that they all want to be left alone. The other Alliances are seeking to rule Tamriel and create "new" empires. The Aldmeri want their Queen on the throne, the Daggerfall want the Breton king and his nigga wife on the throne.
But the Ebonheart Pact, in the lore, are decentralized. Each nation in the Pact is an equal partner, and they agree not to interfere with each other's internal politics. They want to take the throne, and force their Pact system on all of Tamriel. It's basically going to be a confederacy of nations who come together for mutual defense against the Akaviri (as the Pact was originally formed to defeat the Akaviri Invasions.)
Western Skyrim breaks off from the Pact, as does House Telvanni. The Argonians are all-in, because the Hist told them too.
TLDR: I get why TES fans are iffy about the Ebonheart Pact - on the surface it doesn't make sense. But the game really does go into detail about how and why it works, and there are many quests that involve you keeping this tenuous alliance together.