The ironic thing is that he's a massive outlier: the career he succeeded then failed in was comedy writing, an area where most people "succeeding" are pretty much living on the breadline anyway[1], whilst the vast majority only experience failure. And virtually none of it's down to the economic cycles that affect everyone else! He seems to have fallen so fast because he was so successful: he was rejected for being "too expensive" because he'd been so well paid on previous assignments, perhaps took those rejections rather harder than those more accustomed to them and didn't have the willingness (or perhaps the contacts and early-career experience) to fall back on writing advertising jingles, or humorous radio snippets, or co-writing on a large team, until eventually he was so out of touch with the industry Craigslist was his best option. For the majority of aspirant comic writers, Craigslist is the best option they'll ever get to earn a living doing it. Then again, half of them don't write stuff people want to watch...

[1]for comparison, in the UK, "success" as a comedy writer is getting the equivalent of $8,000 per episode total to write a standard six episode series which makes it onto BBC, and then getting another set of six next year before your show gets cancelled. Needless to say, you can earn less from radio, or co-writing, and most comic writers that aren't also actors have other income sources (and smaller families)