Close When used as an adjective, can be used when talking about physical distances.
The grocery store is close. = The grocery store is near.
In this case "close" and "near" can be used in the same way and it is relatively easy to determine that "close means a physical distance.
As a preposition, "Close" can only be used with the word 'to'.
I am close to the library. = I am near the library.
Don't stand so close to the fire = Don't stand so near the fire
Once again "close" and "near" can be used in a similar way and it is relatively easy to determine that "close means a physical distance.
When talking about more abstract concepts, like relationships, then we rely more heavily on the context to indicate the way a word, in this case "close" is being used.
In this example, we could equally assume that
"she's very close to her mother" = "she's very near her mother" or they have a strong relationship.
From the lack of context there is ambiguity regarding the meaning of close. Yes, we could make an assumption, that it relates to a relationship, which may well be correct however it would only ever be an assumption.
Whilst in the statement
"My brother and I have become much closer over the years" = Their relationship has become stronger.
From the context there is no ambiguity over the meaning of the use close.
Prepositions and abstract meanings; prepositions that show relationships of space often have abstract as well as concrete meanings.
"Her relationship isn't good with her father, but she's very close to her mother". = They have a special relationship.
Again from the context there is no ambiguity over the meaning of the use of close as the subject of relationships has been clearly identified.
Therefore it can be suggested the meaning of close in the abstract when used in the preposition "close to" can be misunderstood unless the context clearly identifies the use of the abstract. Which probably explains why
we are less likely to use the preposition-based format in relation to the abstract.
Ref C.E.D. Prepositions: uses