Why is my house wired with two coax in every room and an RJ11 splitter?
Most likely this was a satellite dish hookup.

Back in the 90s, when the technology was nascent, each box got its own LNB feed from the dish. You'd also need an antenna hookup to get local broadcasts (as in two separate cable feeds). The phone line was so the satellite box could phone the company and report whatever purchases were made via the remote (like pay per view)


  It doesn't seem like a pro did the work, especially considering the rats nest of coax in the attic.


In the earliest days you didn't have a whole cottage industry of professional installers like today. Instead, you had a lot of installers who doubled as local sales associates and it was merely a side business for them. My parents had one installed in their rural house in the mid 90s by a man from a nearby town who ran a hardware store. As such, you'd have some strange things done by installers (like using a phone duplexer to join lines).

Most modern installers don't even bother with your attic nowadays. They run it around the eaves of your house, then drop it down and straight through the outer and inner walls.