Many people ask me, “What’s up with hyphens?”
What I remember from linguistics in grad school (many years ago) is that English is an agglutinative language (but not as agglutinative as German). English glues words together. The normal progression is to hyphenate the words being glued together, and then gradually, the hyphen disappears, until the word is spelled solid.
I remember “on-line” and then one day, when I must have been sleeping, it became “online.” If I think about it hard, the deletion of the hyphen is a good thing (if no confusion would result), because it is less cluttered and saves on ink (that last comment is facetious).
Now we argue about e-mail and email, but if this linguistic theory holds true, the loss of the hyphen is just following the theory, as are many of the hyphen deletions that you may have noted.
Of course, grammar books and style guides just state a slice of acceptance in the middle of a linguistic sea change. The best advice is to simply follow the style that makes sense to you at the time and be consistent within the document, department, division, and company.