I think the explanation is rather more innocent. I’m pretty certain China has made up the majority of EM returns over the past few decades, even relative to its size. Hence the demand for ex-China funds has been low. I think most of them are relatively new. EMXG has <GBP200m in funds.
Ex-Japan for example is very popular because the economy is a large proportion of Developed Asia/Oceania but has been stagnant for decades.
Ex-UK has gained in popularity since Brexit, but I think has been popular for longer, perhaps because the LSE is full of multinationals and the different currency.
We just need more IE users to vote for the ex-China ETF - EMXG 