To answer the semi-rhetorical question in the title of this post, because I can. Also, I joined a shanty choir called The Allegheny Bilge Rats Shanty Choir. A shanty choir is a group of people who get together and sing sailing/pirate/working songs, occasionally accompanied by instrumentation.
Which is where the tuba comes in. A few of our songs are quite raucous and needed some oompapa. I was asked by the head of the group if I knew anyone who played tuba. I had mentioned that I had played tuba my senior year of high school (13 years ago, mind you). So we went looking for tubas, sousaphones, helicons, etc to add that special blatting to our songs and I was able to borrow one from my former Sunday School principal. It had been her brother-in-law’s tuba and had been sitting in her and her husband’s basement for years and years. Albeit needing a little TLC, it still works great!
So to really answer my question, I have a tuba because I’m able to acquire one and play it in amusing situations. Isn’t having a tuba a reason enough to have one?