Hozier's built up a huge fanbase in the last few years, he has 48 million monthly listeners on Spotify currently.
They're not just streaming the big hits either, he has 17 songs with at least 200 million streams.
Self Esteem headlined GM in 23. She headlines EOTR in 25. She's certainly no smaller than she was in 23. Its simply never as simple as saying X is playing Y therefore they cannot possibly play Z. Khruangbin heading an already sold out GM25 makes sense for a variety of reasons. Crossover with a 25k festival in London at the height of summer would be minimal. As it would be with a show in Halifax to 6k (as already mentioned, still not sold out). It would be a coup given their recent ascension , but it's absolutely within the realm of possibility.