Signal justifies not allowing usernames as (partially) an anti-spam measure and I assume they also be doing it to limit the amount of accounts created and, so, the use of server resources for which they pay. Selling these accounts solves both problems.
Also allows us to actually use Signal for groups, I don't like the idea of large groups knowing my phone number.
Correct. They are asking money already.
Signal justifies not allowing usernames as (partially) an anti-spam measure and I assume they also be doing it to limit the amount of accounts created and, so, the use of server resources for which they pay. Selling these accounts solves both problems.
Also allows us to actually use Signal for groups, I don't like the idea of large groups knowing my phone number.