When the imams (a.s) say chess is haram to the extent where looking at it is prohibited, do they refer to the chess of their time if in any way it was different or are they referring to the chess of our time, and if the latter why such a strict ruling against it?

Most scholars state it includes the chess of our time as well. Some possibilities:

1- It’s an addictive game, and it can lead to anger/rage
2- Scientifically it has been proven that it alters the brain, and this might have negative consequences
3- It has negative spiritual effects. We don’t know how the spiritual works.