Most people don't realise that BA is the dominant board on FT.

If you look at total posts, you're at 2.9m. For the US carriers you're looking at 1.6m for Delta, 700k for AA, 1.6m for United (although historic mergers and subsequent forum resets may impact this).

Obviously this is an English-language site so you'd expect the dominant airline of an English-speaking country to dominate. There is more to it though - I think the fact that BA is effectively a London-based airline means that we are all talking about the 'same' airline and most threads are relevant to most readers. The US airlines have multiple hubs and so their FT boards are more of a mix of topics. The BA board is also far more lighthearted than the US ones.