Here's why:
* It lacks a verb: Sentences need a verb to express action or a state of being. This phrase only has a noun ("bicycle") and prepositional phrases.
* It doesn't convey a complete thought: We need more information. For example, "The bicycle in front of the store is red."
To make it a complete sentence, you could add a verb and complete the thought:
* "The bicycle in front of the store is beautiful."
* "The bicycle in front of the store was left there by mistake."