The entire point of a "pin" connection is that it does not resist a moment. If you move two parts connected via a pin connection, the parts are supposed to move freely, but rotate relative to each other at the pin.

As such, the moments are always considered 0 at a pin connection. Any load that would induce a moment would cause the frame to move into a different position until that moment becomes 0. The goal is to analyze the frame in this final position. Some frames move dynamically, and in those analysis, moment equations are considered, but not for the purpose of determining indeterminacy.

The entire point of a "pin" connection is that it does not resist a moment. If you move two parts connected via a pin connection, the parts are supposed to move freely, but rotate relative to each other at the pin. As such, the moments are always considered 0 at a pin connection.

Let's consider classical static analysis frames from second year. These always have the loads applied directly to the pins, never on the members. As such, the moment arm is zero, and therefore the moment equation is irrelevant. Now let's consider real world analysis, when a load is applied to the middle of a member. Since the member is considered to have pinned connections, where the moment at each pin is zero, we do not need to count on other members transmitting that load. Instead, that single member that is loaded could be treated as a pinned connection beam. Once the load is resolved, the pins still have - no moments. Again, no additional equations to resolve the indeterminacy.

Note this applies only for static frames. When frames move dynamically, the members can rotate, and this rotation is caused by moments from dynamic movements in the members.