system
Given the following post, respond as if you're commenting on Reddit:
human
[Babylon 5]  Considering all the mayhem that came through the Jump Gate why didn't Sheridan mine the living hell out of the entrance?

Especially during the Civil War period?  Make them command-detonated mines to avoid accidents and B5 is much more secure.  Plus Sheridan blew up the Black Star using a nuke as a mine so it's a familiar tactic for him.
gpt
A number of reasons:

1. Generally, larger warships that warrants mining against have their own jump drives and therefore could avoid using a gate in enemy occupied territory to exit hyperspace. Since mining is a significant undertaking, poses a navigational hazard even when inactive and B5's gate sees very heavy traffic, there is absolutely no way that any of the indigenous powers would not know about a minefield. 

2. Smaller ships without their own jump drives are less vulnerable to mines. 

3. Nuclear mines detonating in proximity to jump gates is hazardous to the gates. One has to remember that hypergates are strategic assets to be captured whenever possible, not to be risked haphazardly. Mining gates would undermine navigation in the whole area, for both combatants and non-combatants. If one doesn't have the ships to defend a gate, one really doesn't have any business occupying that near-gate space.

4. B5 was built with the goals of facilitating diplomacy and trade among the species. Mining the local gate would be politically detrimental to those goals.