Why two front wheels?
-Delta (two rear wheel) trikes need extra chains, differentials, and special wheels for smooth turns. While this is a fine system, tadpole trikes (two front wheels) are simpler and easier to maintain, and new or upgraded parts are available from the stock of your local bicycle shop.
-You can keep an eye on your cargo better.
-It's easier to see if you'll fit between two obstacles without looking behind you while moving forward.
-Front load trikes, from the general public's point of view, are more likely to be seen as work vehicles of some type (and not just a weird in-the-way bicycle) from their long history as ice cream trikes.