Lots of reasons. I’ll list some below, but don’t take offense. This is your forum as much as mine… (as in it’s not either of ours) neither of us make or enforce any rules.
If everyone asked their question without searching I think we’d be bombarded with so many new threads each day it would become dysfunctional. In the past week, I’ve searched and found existing answers to dozens of questions I’ve had. The fact that we’re not being completely bombarded by new threads means that most people are in fact searching for answers, or at least recognizing that their question is not worthy of starting a new thread.
Is unicycling technology really changing so fast that searching isn’t useful? Someone posted last week about plastic vs metal pedals. Has that really changed in the past 5 years, year, month? What’s the lastest? Disc brakes? I’m not really sure… lol, my instinct is to do a search and find out! 
Searching gives you instant results. You don’t have to wait for someone to respond. Would you use google if you had to post your search and wait for someone to answer it?
If others are like me, not all answers are easily recalled. But I do recall seeing the answer in another thread. So to answer the new thread, I find myself searching. Ugh. Why am I searching when the OP could have?
Seeing someone’s current answer in the same thread as an outdated answer from 5 years ago can be very interesting, if not useful.
Not searching and then repeating topics and answers feeds itself. Searching becomes less efficient and less useful with repeated information. Imagine if over 5 years everyone who was interested in learning about the pros and cons of titanium frames posted a new thread and didn’t search, resulting in 100 threads on the topic. Each thread has varied responses. Then when someone does search for that topic they find 100 threads. Thread 1 is good and they learn a lot. Thread 2 is 90% repeated information, but a few new pros/cons are gleaned. Thread 3 is 99% repeated info, and seems like a waste of time to read. Threads 4-41 and 43-100 have no new info. But of course the searcher gave up looking for new info at thread 5 for lack of any new info. They missed the most fascinating pro/con that was buried in thread 42. Had all this info been in one thread, and not repeated, the searcher would get more info faster, and wouldn’t miss any.
I just spent a good chunk of my lunch break writing this. If I thought it was going to be read once and discarded, I wouldn’t have. Hopefully someone a week/month/year/decade from now will search and learn something… if not fact, at least my point of view.
