They absolutely let you withdraw earnings. I place around 20 wagers a day. Pinnacle and Circa are used as measures of what the market is actually pricing in. You can devig lines to arrive at event likelihoods. From there you can line shop such that your expected value is positive over the long run.
It’s not that hard to look at lines at Pinnacle and Circa and make estimates about the fair value of a wager. Open accounts at every book and line shop and maximize expected value.
Also you are ignoring platforms like Novig which are like the polymarket for sports betting.