Tomatoes Started Indoors Not Flowering?

This is the first time to start seeds indoors. Everything seemed to be going fine. I started 3 types of peppers on about 2/17. I discovered they are very slow, but seem to be on time for 5/15 outdoor planting if the weather holds up. I also started tomatoes. These are the Campari variety that I get from Kroger/Meijer's etc. I was told and I watched a video on planting from a cutting of a tomato. I put starter seed in a Jiffy Pot, cut a 1/4" slice of the tomato in the pot and then covered it with starter soil. The seeds sprouted to the point that I had to thin them. They have grown well and I have thinned them down to 4 plants total. I had to transfer them to larger Jiffy Pots, two to a pot. My question/issue is that they were about 12" high on 4/9, today they are 20" tall and spindly. There are no flowers and not all that many branches, but I know that doesn't matter for planting. Color is very light green, but not translucent, yet.

Any help would be appreciated in this matter. I do great outdoors when I buy and plant.

Thank you.