What makes the dictionary decide whether or not a word deserves multiple entries or multiple meanings under the same entry? - Jinx
The dictionary doesn’t decide. Dictionaries tend to be lifeless objects constructed of many sheets of paper with type on them and an outer cover bound to the paper.
The editors would take up that duty. 
Far from a lexicographer here. For one thing if the words come from different roots, such as “homo” coming from the Greek “hom” or “same” and “homo” coming from the Latin for “human” they are two different words.
Or if a word is both a noun and a verb, such as “captain” which is a noun meaning “the leader” and a verb meaning “to lead.”
But you’ll often find entries that say (just making this up here) Captain. n: The Big Cheese on a Boat. v.: To pretend to be the Big Cheese on a Boat.
But then in that same dictionary you’ll find:
Cheese: n. Yummy food made from milk and rennet and stuff. 2. The Big ~: The head honcho (such as on a Boat.) 3. TMI entry deleted for decency.
Cheese[Sup]2[/Sup]: Entertainment of supremely low value or quality. 2. Comedy in this realm.
Cheese: v. To annoy greatly. “The Captain really cheesed me off.” (var: cheezed.)
At any rate, I have been wondering the same thing.
The vagaries of the language often give dictionary builders a hard time.
The examples I gave were just one reason for different entries for the same word. There are obviously others. And technically words that come from different roots or are used as both a noun and a verb are different words. They just happen to be spelled the same; i.e. they are homonyms.
Dictionaries are not created out of thin air. They’re records of actual usage of words in the written language.
All dictionaries start with collections of quote slips, word by word quotations of words used and their context. The lexicographers behind a dictionary will collect literally millions of these quotes. The process of sorting them out into shadings of meaning goes on for years. Writing up the meanings as definitions is an art, and good concise definitions are reused across dictionaries.
The best way to see this process in action is to look at any of the many books on the making of the Oxford English Dictionary that have appeared recently.
Empire of Words: The Reign of the Oed, by John Willinsky
A short version, without any of the flavor of the 40-year process, can be found at Wikipedia.