The popularity of mobile gaming has been on the rise for years, consistently gaining new users month after month. There’s been no shortage of innovation either, as more capable hardware and developers more comfortable with mobile interactions have continued to push the limit of what’s possible on these devices. However, amongst all that innovation and growth one type of game has remained just as popular as ever, and in fact has been around far longer than the mobile phones they’re now being played on.

So, what is it exactly that makes casino style slots games on iOS so popular and addictive?

According to App Annie, as of October 2015 four out of the top twenty grossing iOS games in the United States are casino games, with a full 18 casino style games (poker, slots, bingo, blackjack, or other parlor games) rounding out the top 100 titles. The majority of those titles feature, or are exclusively, slots. Some titles take advantage of specific properties or licenses but many, such as the reigning top grossers DoubleDown Casino and Big Fish Casino, are simply virtual casinos, using relatively simple graphics and sound. Still, there are a few reasons why these games see so much play time and make so much money.

Here are four reasons iOS slots games are so addictive:

Easy to Play
Pull the lever on a slot machine once and you’ve got a pretty good idea how things are going to work out. The wheels spin, images lock into place, and whether you win or lose, you’re just one quick virtual pull away from your next chance. This ease of use gives iOS slot games their immediate accessibility and ensures that they have a broad audience right from the start. Just like in brick and mortar casinos, many games layer on different mechanics such as multipliers and even quest style gameplay, but the core loop is always the same. Pull a handle (or in this case, push a button) and something cool might happen.

One of the better choices in the “ease of play” is Majestic Slots – aimed at Aussie players – a relatively new casino in Australia that also has a mobile version. With offers like Enchanted Garden, Golden Lotus or Ninja Star, the slots games there are fun and extremely easy to play!

Fast and Familiar
The rise of mobile gaming has its roots in convenience, with many players getting in a round or two while on the bus or train, in line at the grocery store, or waiting in the doctor’s office. In fact, according to a 2013 study by marketing firm NativeX, the average mobile gaming session lasts just 1 minute 27 seconds. iOS slots games take the convenience factor to the maximum, allowing players to jump in for a quick spin or two any time, and for those who may spend their weekends in a casino or parlor pulling slots anyway it’s a comforting, familiar way to pass the time. You can win a lot of (virtual) money in a minute and a half.

Low Commitment
Even the most casual of free to play mainstream titles, blockbuster games such as Supercell’s Clash of Clans or Boom Beach, require that that players log in frequently to manage and protect their investment. To really get the most out of the games, you need to form alliances with other players, go to war with your mutual enemies, and spend painstaking hours arranging and rearranging your base for maximum effectiveness. Not so with slots games. They provide a simple, streamlined experience that’s easy to hop in or out of at will.

Strong Hooks
Perhaps the most important factor in their wild popularity is that just like a real slot machine, iOS slots games are relentlessly tuned to provide just the right number of little wins to keep players coming back time and time again. These carefully engineered dopamine rushes are doled out with scientific precision, ensuring that each and every pull of the virtual lever is optimized to keep a player winning just enough to entice them to spend just a bit more for another chance to play and win it all. Mobile developers are sometimes accused of an almost cynical commitment to separating users from their money via microtransactions and timegated content, but they’re only just now catching up to what slot machine makers and casino owners have known for a long time. If you give players a little taste of victory, they’ll keep coming back for more.

The iOS games landscape is vast and growing daily, and there are different types of games for everyone. However, just like in real life slot machines continue to be an engaging, often addictive pastime. Fads may come and go, but there will always be some version of a slot machine waiting for you to take that first pull. Bet on it!