I have seen different palms of them connectors, some of them are positioned at an angle. Why so?

The choice of the connector depends on the area where you will have to do the installation. For example, it is easier to install an angle connector in confined places, as

If the palm is shifted from the central axle of the connector and located lower, you have no restriction in width of the busbar, and you will not have to bend the wire. This type of connector can be called universal in the comfort of work.