Related to water supply. After fruit is more or less developed, the skin "toughens" to a certain degree. If the plants then receive a gulp of water -- rainfall or irrigation -- the extra water in the fruit makes the skin split.
Some kinds are more likely to split than others.

I use compost as a mulch. To retain some water in a downpour, and to hopefully reduce wilts and blights.

One year we got two or three inches of rain in a day. Two to three hundred yellow cherry tomatoes split on just on plant!

When a plant seems to be reaching peak production, I cut back the watering, then pick the tomatoes two to four days later. Then back to the regular watering schedule of twice a week. I try to convince some of the other tomato-growing neighbors that you don't have to (and should not) water once a day. They may not trim the bottoms of the plants, and use compost tea, but they love to water daily!

steelskies, I think your tomato plants ARE healthy! Like others already mentioned. splitting and cracking has a lot to do with the variety and environment. I grow Juliet because of their resistency to cracking and spliting, but they're not to everyone's taste bud, and they're not cherry. For cherry, maybe try Sweet Million?

I have learned a lot from this this thread.

Tell me-- why should we trim the bottom of the plants? When should we do this?

~~Brandy

The bottom leaves are suseptible to soil-borne disease,so the bottom leaves are pulled off .that would get splashed on to. Some people trim them farther up the stalk for better air circulation to dry the leaves or easier to find fruit/

I quit planting Sweet 100's because they crack so bad for me. Pik'em early and the next day still over half will be cracked.
Got to be a better cherry tom somewhere!!!

Reisentraubes seem pretty resistant to cracking. Taste is pretty average, though.

dickiefickle, you are wonderful! You have really helped me! Thanks! :)