aleksl - 4:36 pm on Sep 21, 2009 (gmt 0)

Because they are built by wrong people.

Most shopping carts are either:
1) started by a company hiring someone to build ecommerce solution, or
2) built by inexperienced programmers, or by experienced programmers with lack of GUI sense, or
3) were originally designed to be used for a one type of online business and gradually added features but never thought these features through or piled up so many features it became unusable to everyone

Wrong people driving the development.

IMHO it is RARE that a shopping cart is created by people with experience of three things:
1) programming
2) running ecommerce, and
3) knowledge of graphics/usability

Just because a brick-and-mortar business is hiring a team of programmers to build an ecommerce site doesn't make this duo expert in either of the above.

And of course the fact that there's gazillion open source free carts out there doesn't help, it typically makes it so much harder for someone experienced to enter a niche with a quality product.