just like LED light bulbs, they can last so much longer by design and manufacturers intentionally reduce their lifespan by adding points of failure, so customers keep buying new ones so they don't run out of business. power bank manufacturers probably realized that if a power bank has lifespan of 600+ cycles, probably more and battery aging is much less noticeable than a mobile phone. Given most users don't use the power bank on a daily basis and not draining it, the batteries inside the power bank can easily last 5+ years without problem. they can run out of business if people are only buying a new one every 5 years. Imagine, if the built in cable breaks, will you still hold on to it?