Reasons why online pokers can not just go to a B&M casino and start collecting money:
1. Higher BR requirements. A marginally winning player beating 50NL ($0.25/$0.50 no limit) for 3PTBB/100 who is also playing 8 tables at once (assuming 100 hands/hour, which is somewhat reasonable) for 20 hours a week can make about $25/hr, which ends up to be $500, before counting about $215 in rakeback (assuming 27%RB). So at $715 a week, the 50NL player is making about $35/hr. Similarly, a reasonable enough WR for $2/$5 live NLHE is about $35/hr. The difference? The former is going to call for a BR of 20-30BI ($1000-$1500) to play comfortably. Live, you'll only need 10-15BI, but now you're looking at $5000-$7500. The figures can be even more skewed for skilled online players, who can easily surpass 3PTBB/100.
2. Live poker requires different skills. In online poker, it would be absurd to open-limp with low pocket pairs in a FR game. If you actually end up flopping a set, you will never have the implied odds to pay it off post-flop in order to compensate for all the money wasted when you did not flop the set. Live, the is actually a +EV play and almost a necessary one at that. Most live games at these stakes will have 4 or 5 limpers and the same amount of callers should anyone raise. Profitable live plays would be suicidal online, and many players can't successfully adjust.
I'll make these shorter because I need to start being productive and stop posting on here all night.
3. Rake is significantly higher live than online and there's no rakeback.
4. Travel and time expenses weigh in heavily, depending on the availability of live action.
5. Game speed is excruciatingly slow in comparison, which makes it hard for online players to focus at times. It also means that swings can last a lot longer. And no multi-tabling, of course.
There are more reasons, but these are significant obstacles.
KJ, the UIGEA made it a lot harder to play online, and many sites stopped catering to US players. But sites like FTP, UB/AP, and PS still took US players. It was as easy as loading up money with your VISA card. After 4/15, US players could no longer access their entire bankrolls or play at any real-money tables. Big difference, unfortunately.