NEO is popular in Asia. We do not have kiosks in that region
Only btc I think would be the best option considering the market cap and people who own it is the highest compared to any other coin. So if you place some small coin in ATM hardly few people may use it and to run the ATM we require highest number of footfalls and only btc coin can provide that at the moment.
Plus some regions have specific preferred crypto, like Japan 🇯🇵 and China 🇨🇳