We can and do. Some of them a rectangular or square with trapezoids on the bottom.
Cylinders are strong and make it easy to support the weight, and if you stack it tall it can just be poured into whatever you use to ship it.
Heavy machinery is cheaper now than it was in the past, so if we need to use a different shaped container and use machines to get stuff out, they can do that now without it being too expensive.
All things being equal, people will use the cheapest effective solution. Other form factors aren’t particularly safer or anything.