I had this when I was trying to grow outside in a very small greenhouse. I changed the lighting, tried LED, CFL, a whole range and the pitches still remained very small. I introduced a Humidifier, and noticed the pitches started to develop and form much faster but still many didn't fully develop, but I could not maintain my humidity without keeping the Greenhouse completely sealed. For me it was a catch 22 as I then had temps inside the greenhouse higher than 35 degrees midday and even with a huge industrial fan, i could not keep my temps at around 20 - 25 Degrees, so I had to try another plan. Recently changed to a 4-foot terrarium (Standard 4 foot fish tank), and got the humidity much higher with just a standard ultrasonic humidifier, and the pitchers have exploded in growth.Same lighting was used, but for me, my humidity was too low, and temperatures were too high for my plants. You can check, depending on your plants here as to what temps you need from this past post: