The first three answers (Erk, Mary, astrophobic) are good.
Another approach is to subvert the trope: Provide the bridge, but it is a convenience trap: The bridge is designed to collapse (and perhaps raise an alarm) as soon as somebody crosses the center point of the bridge.
If you want to play it for laughs, the characters have this "too good to be true" epiphany, and all agree to avoid the bridge, and go through hell getting across the chasm, only to find out on the other side, the bridge was just a bridge, everybody uses it.
Or they test it, tie a rope to somebody that tries to cross the bridge, the center falls out, as expected, but maybe there is something salvageable from the remains of the bridge that lets them get across.
Or maybe, they figure out the triggering mechanism, and instead of crossing over the bridge, they can climb across under the bridge on the support struts. More dangerous but still a way across an impossible chasm.
Or maybe, the trigger can be turned off somehow, and they figure that out.
You are still using Bridge Logic; it turns out to be an easy (or easier) way to cross. But it does makes sense if somebody wants to go to or leave what is effectively an island, they need a boat, a plane or a bridge across the barrier. Even castles had drawbridges to safely cross their moats with men, horses and supplies.
So some mechanism being there is not entirely implausible; and it makes sense for characters to seek it out and try to exploit it.