Those that stop Crappie fishing after the spawn, IMHO, are either chasing another species or not wanting to fish for Crappie that are not right against the bank (shallow). They want the "easiest" situation in which to "load the boat", catch the "bigguns", or "get a limit" on most every trip and that's the only way/time they know. That's their choice, and I don't fault them on it ... but, I do agree that they're missing out on the potential to do just that, through most of the rest of the year. They just need to learn the normal movement patterns on their lakes, and adjust their methods to suit. They may also be some of those people that have many other hobbies or sports they enjoy, and just choose to fish during that particular window of opportunity. I'm good with that, too.
I've caught Crappie all through the Spring/Summer/Fall, in years past, by simply adjusting to the weather conditions & the depth/location it sends the fish ... either by fishing from 0dark30 to midday, or night fishing, to escape the heat. I wasn't set up to spider rig or pull cranks back in those days, but still managed to find/catch fish. As I start a new year, now able to spider rig, I'm hopeful of similar results I got from casting jigs.
... cp