Why is there no "e" in Tumblr?

I'm not a very tech-savvy person. I don't know how to use a home computer to its fullest potential, whether it's the use of Excel spreadsheets or storing digital photographs taken with my "cinematic eye". On the internet, there are sites that are tremendously popular, like Twitter, but I just don't have the interest in maintaining my "tweets". Once I thought it would be a fascinating experience to limit one's thoughts on a particular subject matter to a prescribed set of characters, but I quickly gave up because I have nothing profound to express in 140 characters or less and don't wish to telegraph my daily rituals. Yes, many well-known people (politicians, actors, writers, cupcake bakers and pointless celebrities) have Twitter accounts and are followed by thousands of people who yearn for any insight into an individual's daily minutiae. Facebook, which I enjoy, (mostly because it is highly addictive, but also because it does provide a modicum of contact with actual friends and acquaintances without being overbearing or time consuming), is also a forum where people can proudly display their status updates, hoping for numerous replies, craving some form of attention in an otherwise anonymous cyber realm (do people still use "cyber", or is it more of a quaint relic from the 90s, like "information superhighway" and "surfing the 'net"?).

Recently a friend posted on Facebook that made reference to something known as "tumblr" (or the more officious "Tumblr"). I didn't know what that was, though I believe I have heard the term before. I consulted the internet, that veritable repository of instant gratification, and I discovered that Tumblr actually means "tumbleblog", which is apparently a micro-blog, likely that intermediate platform between tweeting and blogging. I haven't come across a Tumblr account, so I still don't really understand what a micro-blog looks like or what its function is: is it for people who don't have the energy to commit to a "full" blog, but want more substance than what a tweet can provide? Lecherous man though I am, I equate "tumblr" with "tumble", in which two people enjoy the close proximity of their bodies in centrifugal motion, so I'm afraid I can't take Tumblr seriously.