Not exactly sure what happened, but I don't think their models were doing well — they had to return investor money earlier this year (https://www.bizjournals.com/boston/news/2020/02/20/fintech-f...)

I still think the economics works — QuantConnect seems to be doing really well — they've been running cash competitions lately. They have even more data which along with backtesting is free, and it also supports live trading for a monthly fee.