OP may be highly skilled and disciplined, but the implication here is probably a bit exaggerated.

Assuming he is talking about buying in a full $500 at a $3/5 table, that's 16 big blinds an hour (16bb/hr x 5usd/bb * 8hr = $640), which is a god-tier rate in the long run.

For mere mortals with less skill and patience, it's also possible to lose the same amount the next 8hr session, resulting in a net zero for two days of work. Or, to sit break even for 8hrs with crappy unplayable hands, because you do need to play less hands to win as he mentioned.

My guess: events are not frequent, at least not in the above commenters neck of the woods. Travelling costs money, so they stick locally.

Variance can suck out any profit from cash games and can get you deeply stuck for months on end (see: any full time poker youtuber). Tournaments are even higher variance.

And if you switch to doing this full time, you become self-employed, which drastically increases the cost of taxes, healthcare, social security, etc. Medicare tax doubles. Social Security tax doubles. You must buy your own healthcare, which drastically increases in premiums (unless you have a spouse who can add you as a dependent on their W-2 sponsored plan).

This really goes for any self-prop business/freelancing. In exchange for freedom of being your own boss, you pay in stress, variance, and taxes.

To make this work, you'd probably have to make double that per 8 hour session. Which is insanely difficult to do as a poker pro and sustain as a "full time job".