Is there a reason for this? Or is it as simple as "online gambling"?
Could you elaborate on this? I'm quite interested by what you say.
I've been out of the industry for three years now, so when I first started working for William Hill it was in 2004. At the time, they were the last of the big companies to be using manual tills, with carbon slips which had two parts to them; it was put through the till with the date, time and stake stamped by the tills on the bottom, and the bets had to be settled manually using a marker sheet and your brain - if you needed more, an OTT or betting calculator was available in every store. Customers used to come in and treat the betting shop as a social environment - cheaper than a pub, and you can have a chat.
With the advent of EPOS tills, bets could be settled quicker, meaning that more and more meetings could be added. Suddenly, the industry went from 4 horse meetings and 3 dogs every day, up to 10 horses, 8 dogs and 7-8 virtual race (random number generating games, disguised as horse races, dog races or motor racing) meetings. The massive influx of meetings and available races meant that the quality horses were being spread thinner and thinner, making the racing crap and unenjoyable. This also coincided with an increase in the maximum stake allowed on the gaming machines, and the speed at which players could play increased - now down to 2.5 seconds per spin for fruit machines style games and 25 seconds per roulette spin.
Traditional punters who would spend the time to study the form and make informed decisions stopped betting because the races were poor quality, and the younger betters coming up have no idea how to read form and make a good choice. This lead to the increase of three types of customers; those who would bet on anything that moved - dogs, horses and virtual racing, basing their selections on prices and previous results (absolute garbage on virtual racing, previous races does nothing to affect the current result); the second type of customer who would pump a week's wage into the machines to play roulette covering the entire board with 5p chips just kill time and lose the absolute minimum; and the final type who are called ARBers - people who cheat the system by attempting to put as large amount of money as possible on horses they have laid on the betting exchanges like BetFair. This works by laying at a higher price but less money than they place the bet at. Doing this guarantees them a profit because they try to ARB in as many bookies as possible before the price moves. The social element of the betting shop still exists, but only within small groups, and by shouting at each other over loud machines and louder commentary.
With loud machines and and louder customers, traditional customers were driven away from the stores - combined with shops that could take tiny bets on decent markets thereby limiting the customer's ability to place decent bets - drove the decent punters away, leaving only the three types above. By pushing customers online, it means that the betting companies can run their stores for less, and even close some down in affluent, betting-based areas (poorer areas tend to have more machines punters), meaning they can make more of a profit. This means online offers can be much better than in-store.
Add into this the permanent Sword of Damocles hanging over the head of every member of staff if they don't ask for age verification of mystery customers and being sacked for it, made significantly harder because most of the time there is only one person on shift with a cashier for three hours of the day, and the industry now is thoroughly unpleasant place to work in. I miss the old days of betting, but they've gone and are not coming back.
TL/DR; greedy betting shops forced the punters online.