Speaking as someone who follows the preconcillar fasts, I am not forcing my view, but will offer my perspective. 

A lot of the scrupulosity comes from some regarding fasting as a prayer, not just a personal one but a corporeal prayer of the entire Christian body. Just as we have fixed prayers for corporeal worship we also have a fixed fast, if that makes any sense.

The spiritual aspect is there, but the focus when people come online is on trying to do things right, the same way someone praying the rosary for the first time might seek advice on practicalities rather than meditative aspect which are the real "meat" of the devotion. Likewise fasting itself is more of a frame, and the true "meat" from fasting comes once you go from how to why. 

There is also the fact that nowadays there is little help to find in pastoral guidance when it comes to asceticism/mysticism in the west. The East can expect great help from their priests when it comes to this.  Rules are a pedagogue not the ends