Here is what I think:

With limited garden space, most of us cannot rotate, like some farmers do. And luckily it is not a "must do" thing. As long as you keep amending your garden soil (w/ compost, manure tilled in), fertilized when needed, then you should be fine. Soil is just a housing for plants. They need food and drink. One can grow aeroponically, hydroponically ( w/out soil)

As far as diseases, most are air borne ( blights..) some are viral. There are soil borne molds and bacteria too. But rotating
is not going to eliminate those. Just keep lower part of your plants trimmed (nothing is touching the soil) and there is enough open space for air movement. PLUS (very important) spray your plants with fungicide SYSTEMATICALLY and regularly (about once every other week or so). It is better to prevent than try to fight the diseases.

Seysonn

This may be off the wall, but nematodes seem to capitalize on un-rotated tomatoes. How are the roots looking on those weak plants?

I did not look closely at the roots when I was discarding them, but what I noticed at the time is the large amount of root growths on the bottom of the stem - up to 4-5 inches from the soil.

Actually, now that I remember, it is generally tomato patch, but I had a couple of chives in the question spot. Could it be a problem ?

Some of us can not rotate. I rent community garden space and even if I move around a bit most of my plants are nightshades- eggplant, peppers, potatoes, tomatoes ...

I can grow "other stuff" at one end and tomatoes at the other. Other stuff was bush beans, pole beans, cukes, garlic, beets, and other nightshades.

I grew tomatoes at one end for at least 4 years, then planted them at the other end last year for a great fresh start, only to get Late Blight (or was it that grey mould?) I never saw anything that looked mouldy and it wasn't fast-moving, but had patches of black on the stems and some of the fruit looked decidedly Late Blight-ish.

What the heck should I do next planting season????

Linda