3 reasons without going extremely in depth.
#1 ) its the first of its kind a blueprint. before that producers would do collaborations with MCs. illmatic was the first and most intense version of the standard album that is created today.
they take all the hot producers and put them on one album.
#2 ) your trying to recapture an essence of history by re-listening but its deeper than that. since you didnt live the experience then you can only leave it up to the heads like me who bumped nas albums when they dropped.
this is the type of question of re-living the past/trying to alter history and perception amongst other people your age who are inclined to agree with the older ones who lived it.
#3 ) illmatic is the realest album of all time. every classic you mentioned by mobb deep, biggie, 2pac, mos def etc contain large portions of fictional elements. illmatic is not the only, but it is one of the first albums that was 100% accurate as far as an artists life portrayal.
the only times nas penned a fictional line is when the bar contained what people would later call "shock rap". also being the forefather of that style he is a living blueprint as far as rhyme structure and content goes.