because using the term "spyware" to mean "any time the someone gets information that someone may not want them to have" makes the term apply to silly situations like "I want to search google, but I don't want google to know what I'm searching for"
Diluting a term to cover lesser problems means you now have no term to cover the severe problems.
There is a real problem with apps claiming to be for one purpose, but sending a lot of your information out. Since they actually do work for the purpose they claim, calling them "Trojans" doesn't really work, the term "malware" is so broad as to be meaningless. Spyware captures these programs perfectly.
but if you use "spyware" to cover cases where information gets sent that is needed for the functionality that's being provided, your browser is "spyware" because when you search for something it sends the query you are searching for to the search engine.
See also chicken little, the boy who cried wolf, etc.