Being attacked can’t take place too often in a clash-like. You spend time making a strong base to defend your gold, which is pointless if you’re unexpectedly attacked 30 times before lunch. The fix is a simple timer after each defense: “you’re not in the attack menu until 4pm”. That works fine.
But game designers are a superstitious lot, and they like money. The original Backyard Monsters had a hideously complicated set of rules for when you got a “shield”. Clash of Clans didn’t know the secret sauce and just copied everything, including funny shield rules. And shields are good business. They generate more fear. “You’re about to lose your shield” sells more than “the routinely scheduled attack is coming up”.
Variable shield lengths is the stupidest rule. If an attack doesn’t hurt you very badly, the next attack comes faster. That’s terrible. Better base designs got attacked more often, resulting in more gold loss. In response, players learned to build medium-bad bases. That was as much fun as it sounds. But variable shield lengths adds terrifying randomness. Overnight you could expect 2-3 attacks, but could have lots more, losing even more gold than if you’d been simply steamrolled twice.
The next stupid rule is shields vanishing when you attack. If your next scheduled defense was at 6pm, but you play the game at noon, you get attacked as soon as you quit. Why? This has been changed to merely move up the next attack by an hour or two. Again, why? If you should be attacked 3 times a day, why should that turn into 4 or 5 or 6 if you play the game at the wrong time? Money. For free, players can attack every 10 or 15 minutes: close the App, do something else, then come back. Shields breaking ruins that — it triggers a pile of extra attacks on you. You should buy a training time speed-up.
A really crazy thing is how Supercell’s other game is so fair about attacks. Each day a set few people are allowed to attack you. They either win, eventually, or give up, getting nothing. Every day you defend against 2 people, rain or shine. But as you might guess, Boom Beach is far down on the top-grossing charts.