Let me see if I can write about 400 random words about this.
People reg crap because crap rolls downhill. You see, much like in the corporate world, you delegate to the lowest level. So at the top you have the CEO of the domaining world. That guy owns lots of things, but he got to the top because he knew the best way to control sex.com. His salary is based on this formula: Teenage boys+Parents Gone+Access to internet=random searches and clicks at sex.com.
Below him, are the upper managers. They control the next level of domains. Your 4-5 letter generic .coms, your three letter .coms, and a whole lot of porn sites. They make their money on the porn sites that the teenage boys eventually end up on.
Next is middle management. They run the .net area. They dabble a bit in the .com 6-10 letter generics. They make their money selling pictures of their "cousins" to the porn sites.
Below that is lower management. These are the guys that actually run the show. They do the hard work, they scramble with designs, they actually control the guys who build the websites. The handle the two word generic .coms, the ok .nets, and a whole bunch of deviant porn sites that the upper management don't want to get involved with. They make there money from subscriptions to their porn sites by the upper management.
Then there are the worker bees. They do a alot of networking, own LLLL.coms, some great nets, a whole lot of info and sometimes get a decent porn site going. They make their money selling a few, a bit of adsense, and dumb luck. They control the middle market of sites worth about $450 and up to $8000. They make their money sending referrels to porn sites.
That leaves the people that clean the toilets and take the trash out. They register nonsense, but have the occasionally good month with a few names that were random. They make random sales from $1 up to $449. They may get the occasional $3500 dollar sale, but it is only enough to make them keep registering things that are weird or so random that no one else would touch it.
Crap rolls downhill. By the time it gets to the bottom, people are desperate. They look at one trend and take it to extremes. 888888.tv is an extreme that is unlikely to get the guy that cleans the toilets willing to pay $1 for it.