Early blight is caused by fungal spores getting on the leaves of your plants. These spores live in the soil in your garden and from the soil of surrounding areas. Mainly the spores are splashed up on the leaves during a heavy rain or overhead watering. I think that this year the entire US has had very different weather pattern than from last year. Tons of rain and fluctuating temperatures. A lot of gardeners are having the same problem. Farming/gardening is just another way of gambling. Sometimes you win and sometimes you don't. It's nothing you did or didn't do.
Your plants look great. All of us gardeners are trying to do the same thing and that is to keep our plants alive until harvest. If the weather changes to dry and sunny it will slow down early blight a lot. Next year if you will cover the soil about 2 inches deep with mulch it will greatly reduce the severity of the blight also. But this year with so much cloudiness and rain I guess we are lucky the blight isn't worse than it is.
