I am wondering why ISIS built and/or took control of certain highly visible infrastructure that the U.S. and allies are now bombing, e.g. "four checkpoints, two guard towers and a command post." Surely ISIS could have foreseen how easy it would be for this type of infrastructure to be targeted and destroyed?
IS needs to control the ground. That requires controlling local strongholds, high points and other tactically important items. Checkpoints, guard towers and command points are that - and if THEY don't control them, their enemies will and use against them.
IS doesn't loose too much from US bombing them. A couple of low-level grunts get killed, in exchange for visibility and recruitment and branding ("We are important and strong enough to tangle with America and the West and Crusaders and Zionists... wait no, Zionists are actually wily enough to stay the f^*k away from the area but we'll lump them in anyway 'cause that plays well with the locals")
They still need somewhere to sleep; and somewhere to provide cover and provision for ground combat. Whether ISIS needs fixed infrastructure at this stage is unclear, but they are hardly going to say no to Iraqi and Syrian assets they overrun.
For all we know the coalition is also bombing vehicles and troops running around outdoors. But that makes for a less concise soundbite.