The betting industry over here in the uk has drastically changed and evolved into a different beast in recent years.
Since FOBT (fixed odds betting terminal) machines were introduced over a decade ago, the focus of high street betting shops has gradually centered more on these machines rather than over-the-counter betting (sports. horse and greyhound racing) due to the much higher margins.
Someone coined the name 'crack cocaine of gambling' for FOBT's, as they attract the lowest common denominator of today's society - especially in poverty stricken areas - where junkies, problem gamblers, and low-lifes in general, flock to punt whatever disposable income they can scrape together from their low paying jobs, government allowance, and in many cases their life savings. The type of people who have little to no personal resolve, as they lack the discipline or control to stop themselves from compulsively sticking another 20 into the note dispenser out of sheer desperation - let alone know what a stop-loss/win is - even if it means dipping into their food and rent money, consequently leaving them with crippling debts and depression to boot!
Standard roulette is the most popular choice as it gives the customer the best chance of winning (~97% average payout: categorised as a B2 game due to the relatively low house edge), besides blackjack (>99% payout according to correct strategy) which most people aren't interested in as they don't know how to play optimally and thus would lose much more at as a result. Slot machine games are also popular, and are categorised as a B3 game whereby the average payout tends to vary from 88-94% depending on stake and game: these games are marketed and pushed more aggressively, with many incentives offered to lure in the recreational gambler.
Gone are the days when a shrewd punter could walk into a bookies and place >£100 bet on sports or racing without being profiled and subjected to bet restrictions if they are deemed a profitable bettor. In the past a bookmaker would take the bet first, then decide if it needs laying off; nowadays bookmakers simply aren't interested in taking large bets because the average margin pales in comparison to what they make from the unknowledgeable, weak and vulnerable types shoveling tons into the roulette bandits and letting it all spin.