It's possible they would have been more difficult to pull off in Lego form as well. Them being easily accessible doesn't mean necessarily they are the best choice. The have base Mario and the Fire Flower, and then very popular alternates with Propeller, Cat, and Builder. Wrecking Mario hasn't been around for AGES. It only makes sense to include Builder Mario. I trust that Nintendo and Lego worked together to determine the cross-section of popular, able to be done well in Lego form, etc.
I'll disagree on them sucking. I enjoy them personally.