They tried and look what happened. Engi/BS everywhere.
Tailoring/Engineering look balanced on paper. Their PvE DPS contributions probably math out to be equal on theoretical level. What happened was an unpredictable trinket/CD/proc stacking meta developed which focuses on massive burst periods and comparatively low sustain periods. So now the Engi bonus, which can be controlled and always put inside this burst window, is much better than a random proc which may not occur when you want it. It's very hard to predict these type of things, so I guess they decided better to just remove them entirely.