Simply put the angle of the bogie or truck is determined by the requirement to fit the retracted gear into the smallest space possible especially on aircraft like the B747 and A380 with 4 main gears. See the following-
707, DC8, DC10, MD11, L1011, A300, A310 all had main landing gears installed vertically with the bogies held 90 degrees to the main strut.
767 has a nose down tilt to the bogie but the 757 is level.
The 747 wing landing gear bogie is at an extreme angle so it goes into the wheel well across ship and not fore and aft thus reducing the length of the wheel well required.
The 777 has a nose up tilt to the bogie when the gear is down but transitions to a nose down tilt during retraction to make it fit into the wheel well with the long bogie parallel to the centreline.
The CV880 had a slight nose up tilt but the larger CV990 had a nose down tilt. Convair's explanation for the difference was it was simply a clever change in geometry to enable the 10 inch longer main gear on the 990 to be squeezed into the same space whilst being attached to the wing at the same point as the 880.
The A340-500/-600 has a centre gear with nose down bogie tilt and the wing gears with nose up tilt purely a result of having to squeeze a 4 wheel bogie into the space previously occupied by a 2 wheel landing gear on the A340-200/-300.