BT136 TRIAC not closing on LOW signal to the MOC3021
You are missing the concept here, yes.  Triacs (and SCRs) have a strong positive feedback effect internally: they can be turned on with gate current, but not off.

To regulate power to a light bulb, you need to change when the gate is turned on -- the later in the half-cycle that you turn on the gate, the less power the bulb gets, and the dimmer it gets.

Note that this all may not work with LED and CFL bulbs -- I've kind of lost track of the magic that they put in between the base and the active elements, but I know they don't necessarily like dimmers.