Their performances have been insignificant, to put it mildly. None of them has done or even said anything that is of any particular beneficial significance to the ordinary Singaporean. But they keep getting ministerial positions for the following reasons:
1. Keeps the military leaders happy and hopeful, and hence there will be practically no chance of a coup.
2. Sinkies are easily impressed and impressionable, many Sinkies will be impressed that so and so general has become a minister, thinking that they must be damn great in some way. Obviously, they are not.
3. Having spent their entire lives in the military, they tend to be of a certain mindset, i.e. obedient to their bosses and willing to take orders, less worldly and global in their thinking and analysis, lacking innovation and commercially viable ideas which will be of benefit to ordinary folk. They are hence not a threat to the pervasive groupthink pappy mentality. Look at Toothpick Zorro Lim for example, don't forget that he was a Colonel in the military before he went to EDB and then became a minister.