I've always regarded the 'golden age' of first-run syndication (roughly 1986-95) as the period of time when producers finally realized that they could keep a lot more of the profits if they circumvented the networks. Production companies had been forced to grovel to the network heads for decades, begging them to pick up their shows, and watching the networks haul away the majority of the profits from the more successful shows. There had been first-run shows available for long before the mid-1980s--Hee Haw being notable for its success in the country-music genre and its longevity. But the system really blossomed in the mid-1980s because of the boom in talk shows in daytime. Hosts and producers of those shows decided to sell the shows directly to stations rather than relying on a network to distribute them. Local stations had large blocks of their broadcast day that was not filled by network programming (mornings, early evening, and late fringe past midnight), and talk shows were preferable in that period because of the exploitative content and 'star power' of many of the hosts. This was preferable to sitcom reruns or local news. Hosts like Oprah owned a chunk of their show's profits, and as she (and others) became rich and famous a lot of producers saw that cutting the networks out of the equation might allow them to keep more of the profits from a show.
Also in the mid-1980s, there were a lot of independent television stations--that is, a station not affiliated with CBS, NBC, or ABC. They relied even more on reruns of old movies and off-network programming. The Fox Network came along in 1986 but originally only aired original programming on Sunday nights. Independent stations that decided to become a Fox affiliate had to fill up their days and nights with content, so there was yet another demand for various programming. Many of the syndicated shows that aired weekly (as opposed to daily like talk shows) looked and sounded just like network programming and had the same high production values, so the independent/Fox-affiliated stations now had the chance to carry a few more original shows, not just reruns of the other networks. The producers of these shows also pre-sold large chunks of the advertising time that was being aired, allowing the independent channels to go 50/50 with them on ad time to have their local commercials airing alongside national brands, which is preferable to having your commercial time being dominated by cheesy ads for record albums, Life Alert, and Ginsu Knives.
In the early 1990s the first-run market expanded into action/adventure hours, a mix of standard crime dramas and sci-fi/fantasy shows that the networks tended not to have much faith in. This move was likely based on the success of Star Trek: Next Generation, which was syndicated rather than a network show. Shows like Forever Knight, Highlander, and Viper popped up with huge (for that time) budgets, and though I think FK began as a TV-movie on CBS, I don't think any of the others ever even approached a network about airing the show. They knew first-run syndication would give them more artistic freedom as well as "financial freedom" to spend a lot of money per episode. I recall reading that Highlander had a highly unique co-production deal between US, Canadian, and French companies that allowed the show to film half its season in France and half in Canada, giving it a cinematic look that could never have happened if it had been on a US network.
I can't really pinpoint why first-run syndication comedies did not continue to be produced after about 1993. Maybe it was the move toward dramas on the networks, or maybe they did not have as many stations airing them once Fox expanded their programming to seven days per week. Many of the original comedies had run their course, but they were not replaced with others. I know some cable channels had matured enough to produce their own originals (Lifetime Movies, for example), but those channels didn't do sitcoms, either. Court shows took over for many of the talk shows that got cancelled (and are just as profitable, apparently), and of course there are still plenty of sitcom reruns to buy. Reality TV also took some of the time away.