Earlier quoted context omitted.
If they sold Tethers for $1.00 but bought them for $0.99 that would effectively amount to a 1% fee that would maybe give them some profit.
Why would anybody buy Tethers for $1.00 from Tether if someone else is selling them for $0.99?
Note that it does not work this way currently since normal people cannot buy/sell directly with the Tether treasury at all.