Considering they only have “hundreds” of paid users despite how much money they’ve likely burned through, I’m guessing they just couldn’t raise enough additional capital to keep the lights on.
I think it's interesting that they note they have hundreds of customers but their home page says it's trusted by thousands of companies. Are all these companies on a free tier?
I would imagine it's the usual SaaS marketing embellishment, e.g. one Google employee used the software on a trial at some point === "Trusted by Google"