Two reasons.
My main hobby was computer gaming, I'd migrated from RTCW-ET to belatedly joining WoW at the end of vanilla content and got into raiding with my first guild during The Burning Crusade. I'd later migrated from that into a raiding Guild. Swapped from Hunter to Prot Warrior, and became main tank. It had downs and ups and going from T4 to T6 content improves your gameplay. T6 and T6.5 was 'just' cleared before Wrath of the Lich King, but by the time ICC came along it was becoming less fun (even with a fresh guild due to arm twisting after quitting), and eating up a lot of time for serious raiding, with little people on their way. I'd always wanted to write and the itch grew.
I ended up spending a week in bed, tripping on hardcore painkillers after trashing every ligament and tendon in my foot. The first set of laminate floor in the bedroom wasn't great, and the plan was to add a new darker set, before a new bed arrived. The old stuff came up easy, but being a plonker I managed to fall over when chucking the old planks in the garden. Rolling around on a pile of loose laminate planks with one functioning foot, is probably as close to resembling a beached whale as a human can get. At least no-one saw-or laughed-at the fat bastard sliding around for a few minutes trying to get up. As the ankle hurt and 'being too busy to do anything with it' I stuffed on a pair of hiking boots and got on putting the floor down. Halfway through it was still hurting, so I added a bit of duct tape. That may have been a bad idea as my foot became a shrek foot when tape and boot came off with weird wobbly green and purple bruising for good measure. While it can look like a foot with a chicken breast on it it isn't much use. Cue bedridden for week with elevated foot, tripping on pills and getting freaked by something in the room. After three days I figured out it was the net curtain flapping in the breeze, and looked for a diversion. A map, rough nations, list of characters and most of the first two parts of the Tryphon Odyssey were knocked up.
Afterwards I went back and redid 2/3 of the map as the place names I used were Saxon, not Norse and spent time reading up my old university books, new books, wiki articles and resurrecting what I'd learned in History, Archaeology, Nautical studies and finding new points of interest in creating a setting taken around 1000BC and throwing it somewhere else around Warcraft Raiding. That somewhere else has magic and other races. Once you remove the impact of Christianity, and an unroman western europe it is surprising how limiting original sources are for a period, and the same occurs in Pre-Spanish Central America. Evidence occurs, and is being improved upon every year, but it is limited and either here-say in non-contemporary accounts, or with some form of religious or modern bias with the lack of longevity for oral cultures. It is limiting, but great for fiction in being so open to interpretation.
It is very easy to go down a rabbit hole with world-building. Religion, cultures, social structure, races and the denizens of whatever you create can take shape as new, based on something, ripping the piss out of something, or being created in minute detail to stimulate and awe in the vein of Tolkien. I compromised by research reading at lunch, general reading in the evening and Audiobooks/Music at work. That delusion is three lots of research in digestible lumps to the creative pot. Odds are most of that time spent will reside in your head, and what is on the page is minuscule in comparison. Editors and feedback responses (in my opinion) strip out content as it is irrelevant, slows down pacing, bloats description, and the hard one to learn-not bringing anything to the table. I compromised by research reading at lunch, general reading in the evening and Audiobooks/Music at work. That delusion is three lots of research in digestible lumps to the creative pot.
Cue whimpering, but often it is right. Tolkien's outbreaks of singing, while accurate in campfire entertainment get right on my moobs, David Rintoul going on for a few minutes describing a wartime harbour in a Douglas Reeman audiobook, is a bit much, and Pratchett used little description. I guess that is what is meant by 'finding your voice'. That initial pad became a further twelve around Warcraft and children. That original sketch map and sketch of Tryphon became CAD maps and drawings, and later became cover artwork and a wonderdraft map. Both are based off historical technology and cultures, evolving in an alternate reality and have their own fantastical twist and I hope provide entertainment to someone other than myself. World-building is great fun, writing can be evocative and frustrating and editing can be never-ending and a downright headbanging experience. Even so, it is better than tripping with a wobbly foot, and I hope I have learned enough to get the next book out faster, and not be surprised at something I don't remember writing...