Missed approaches are not just generated. It happens when an aircraft is not properly vectored before issuing landing clearance. Aircraft should intercept the localizer at a 30 degree angle (simulator allows up 60 degrees) from the runway centerline from 5-10 miles out and no higher than 3000ft AGL.
Once an aircraft is lined up on approach, it will adjust its descent rate based on altitude and distance from the runway. For example, if an aircraft is 10 miles out at 3000ft, it will descend at a comfortable rate. If it's on a 5 mile final, the aircraft will have to compensate at a steeper angle/rate. However, if the aircraft is too fast (even at minimum landing speed) it won't descend in time and a missed approach will a occur.
If you put a DHC-8 on 5 mile final at 3000ft, it will make it to the runway at minimum landing speed. However, do that to a B738 or a B744 and it's not going to work.