First of all because there is no mystery to discover. From the very first chapter is all square. And rare elements which are not clearly set are guessed right away. Also guess how the protagonists will escape. "The sign" is more a Hollywood script or action is omnipresent.
Again this is something that bothers me. An average person finding himself in an unusual position, is capable of beating repeatedly men guards and highly trained military ... not credible. Like elsewhere history or condition is absent, did not react.