I suppose it depends on what you mean by “recently.” Registration was made optional by the Copyright Act of 1976, so that’s 35 years now.
On the contrary, a lot of clickwrap agreements have been found to be exactly the same as signing a contract.
I can think of a few reasons. If a person is posting something that a boss might find objectionable, s/he might want to use a psuedonym. Posting as tmarcl, for instance, allows me to say things about the Navy (not yet on this board, but I have on others), or about religion that I might not want my real life associates to know about (as it might affect my workplace relationship with them).
To use a more extreme example (which doesn’t apply to me, as I’m fairly mundane), a person could be interested in what’s considered a strange fetish (like furries, or BDSM, or even M&M porn (don’t hate)), and want to have the freedom to talk about it without people they know finding out.
Simply put, some of us feel that what we do on the internet is our business, and no one else’s. Using a psuedonym allows us to keep it that way.
Marc
Edit: I made up the M&M comment on the spot. Just for the heck of it, I googled “M&M porn,” sure enough, there were 654,000 hits. Rule 34 reigns supreme!