Running a public service like this is a genuine commitment to fight spam, malware, phishing, cp, and various other oogy boogies simply because if you don't people will take advantage and your links will start getting flagged as sketchier and sketchier. It's a hard laborious problem to solve when you have to prevent and suss out bad content while also not being able to see it. Bitwarden is gonna be leaning hard into the account requirement and the reputation of the sender.