This happens, in part, because even among scientists there can be different usage of these terms. Of course, to the general public, these terms have very different meanings and connotations. I suggest that you look up the definitions of both words in any English dictionary. Furthermore, both scientific laws and scientific theories could be shown to be wrong at some time if there are data to suggest so. Most scientists aren't trained to critically analyze the pros and cons of laws or theories outside our field.
Scientific knowledge is strengthened by people questioning what is or has been accepted.
Here are a couple of definitions of each word. A set of observed regularities expressed in a concise verbal or mathematical statement. The abstract principles of a science as distinguished from basic or applied science. Look above at the last definitions under Law and Theory. These definitions clearly differentiate the two words.