My guess is partially what vardaro mentioned (to hedge their bets), and partially because the space is really, really "wide" (not sure if that's the right word) in the sense that products like this could go in a million different directions... for example: email marketing, CRM, session reply, chatbots, etc. etc.
That's to say, even though Papercups and Chatwoot seem pretty similar at the moment, I wouldn't be surprised if that changes quite a bit in a year or so!
(Also it's no secret that YC invests in a ton of similar companies :P e.g. our batch alone had at least three video conferencing companies iirc.)
That was backed last year. Isn't there some conflict from the investor when the companies are so similar?