It's less a matter of security and more a matter of consistency. MS's/Apple's rules are geared towards ensuring apps don't affect battery consumption too wildly

It's less a matter of security and more a matter of consistency. MS's/Apple's rules are geared towards ensuring apps don't affect battery consumption too wildly while in the background. Android has no such restriction, and any app you have installed can decrease your battery life significantly even if you do not open it. The advantage of this, of course, is platform flexibility. The disadvantage is inconsistent app behavior (battery is drained by background apps).