Having lit the discussion touchpaper, stand well back!
The reason you need so much is that in a 2- stroke you have no sump with a bath of oil to keep things moving. Think of it this way, at the price of the petrol you are displacing, it's not as bad as it could be!
There are three trains of thought on here regarding oil:
1) As long as it says TCW3 on the label, it'll be fine.
2) Has to be branded, for a multitude of reasons that I won't re-iterate here.
3) Buy it in bulk & I'ts nice & cheap.
Personally I like Yamlube, and can get it in voluminous quantities from the local chandlers. I have also used Quicksilver & a "no name" stuff when Yamlube wasn't to hand. I felt the others are a bit "gloopier" and the Yamlube seems to burn cleaner, although that might be down to what I was using the boat for at the time I was using the other oils.
Do a search for "bulk oil" - you'll find all the other discussions.