Why? Because they aren't really my style. I don't really like "purses", but rather utilitarian bags that I can carry a book, water bottle, notebook, knitting (of course), and maybe a drop spindle & extra fiber.
Now, Timbuk2 messenger bags or Eagle Creek bags are more "me". And I use those on a regular basis and it fits everything that I want.
For day-to-day carrying projects: knitting projects are placed in Stuff sacks (aka Ditty bags) then placed in the main bag. The stuff sacks are often made of rip stop nylon so needles don't poke out, and the bright colors make them easy to find. I have several in different colors so I can easily grab a project and "go".
-- Notions are placed in a small clear plastic makeup bag.
-- Fiber is placed in zip lock baggies
-- the spindles are placed in camera lens bag or wine carrier case (which I found at a local thrift store for cheap!)
However, I did pick up one bag, the Nantucket Knitty Bag, which has worked really well for me thus far. Currently, I use it for long extended road trips in the car or for taking projects with me to "Stitch & Bitches".
The original bag was designed for use by carpenters who need all those pockets for tools, but it works really well for placing all of your knitting & spinning supplies in as well!
(The photo is from the manufacturer site. My Nantucket is black.)
The bag measures: 15" x 10" x 6" with 1.25" handles. You can sling it like a shoulder bag, or close up the top and use it as a back pack. You can also reverse how it zips up so that all the pockets are in the inside of the bag. (I did this when visiting a house with small children).
It easily fits multiple projects, multiple yarn & fibers, and has wonderful pockets for putting in things such as full-size scissors, measuring tape, etc. It's easy to pull things in and out of it, and I can stuff it relatively full without worry.
I've been using it for car trips. For one week-long trip I carried: three sock projects, a sweater project, a hat project, all the associated yarn for said projects; two spindles and fiber for spinning. Then all the assorted tools that got placed in the pockets. It fits nicely at my feet on the passenger side, and the wide open mouth lets me immediately place in a project without any fuss.
When I'm not using it for car trips, it just simply holds yarn or fiber or whatever I'm currently working on at that particular moment, and will often get carried room to room when I'm knitting. (This is an addition to my static yarn baskets that sit by my favorite chairs.....)
The only thing about this bag is that, depending on how full you stuff it, the top won't cinch close all the way, and if it topples over, you might spill your yarn/fiber/projects out. However, I don't normally stuff it that full, so this hasn't been a problem for me.
Overall, it's a lovely bag to use.