Rotten radishes

Another vegetable that's not doing so well--- first the beans, then the squash, and now the radishes. The tops have been yellowing, so I pulled a few up to see how they were doing. I think they've been in the soil so long they started to rot.

Why'd they fail? I think our soil compacted too much, and it's been way too hot here. We'll pull these ones up and plant a new batch elsewhere.