Just checked the Betfair NRL Premiership Marking $896,000 in pool. That is just one agency and just one of the markets. Tonight's game already has $25K in the Pick The Winner Pool, 10 hours before kickoff.
The pools are large and growing. But you are right a large best will attract attention.
What I don't understand is how they get their money on. The pro punters I know have strict limits on them, one guy is only allowed $500 win bet maximum with NSW TAB. All the corporates like Bet365 and William Hill bar you as soon as you win. Some TAB venues, pubs or clubs, also have limits on them, if someone is winning heaps the TAB put a limit on the bets and it applies to all customers.
I know the TAB's and Corporates have customers they call "whales" who are constant losers and they can bet without limit. Often these customers are money laundering or getting rid of excess cash legally.
The Holden Cup is the place where there is money to be made, just follow the money.