For the same reason why livecoin didn't let izoomrud to withdraw his coins. (yes again with that livecoin shit)
I don't get this angle "why would a big company like this would ruin themselves for pennies?"
Wasn't pennies for Livecoin. With XMR and MONA losses they were likely insolvent so they punted the loss to users. Essentially they didn't have the coins, they were trading fakes and eventually removed the markets altogether.
Not to mention the predatory language in Livecoin's terms of service. IIRC it was something to the effect of "if you complain about us in public, we get to keep all your money." There's nothing of that sort in Sportsbet's terms and conditions.