3/4 time is grouping 3 beats per measure. 1 2 3 1 2 3 1 2 3, etc. = 3 Counts per measure
Triplets in 4/4 time divide each 4 beats into thirds. 1 and a 2 and a 3 and a 4 and a. = 12 Counts per measure
In both cases you have groups of 3. However......
3/4 time is a grouping of 3 beats. 1 2 3 = 1 Count per beat = 3 Counts/measure
A triplet is a grouping of 3 subdivisions of one beat. 1 and a = 3 Counts per beat x 4 = 12 Counts/measure.
It's counting groups of beats (3/4 time) vs. counting subdivisions of beats (triplets).
Time Signatures (3/4,4/4,etc) tell you how many beats to count in a measure, but nothing about how to subdivide those beats (or even if you will need to).
8th notes (1 and = 2 counts), triplets (1 and a = 3 counts) and 16th notes (1 e and a = 4 counts) are subdivisions of a beat.
Numbers are used for beats, "syllables" (e, and, a) are used for subdivisions of a beat.
**The number of beats/measure x the number of counts/beat = the number of counts/measure.**