The above indicates that there is/are a lot of N: N is repeated many times; there is (almost) nothing but N. The use of ばかり conveys the speaker's feeling that it is not very desirable for someone/something to be limited to N.
There are only rice fields around the house.
It keeps raining every day.
My teacher asks questions to nobody but me.
Are all the students Japanese?
I only buy inexpensive things.