They cover this pretty substantially in the post on Signal's website (I know they merged the Wired article into this one).
Signal is trying to compete with the richest companies in the world; including for talent. And considering Signal's origins and motivations, they're not going to lower salaries or decrease benefits because some people believe that working for a non-profit automatically means lower compensation.
Signal is trying to compete with the richest companies in the world; including for talent. And considering Signal's origins and motivations, they're not going to lower salaries or decrease benefits because some people believe that working for a non-profit automatically means lower compensation.