I guess it will just depend on what they have to sell, if they can fill a 30 minute block with BS about it, and if there's a market that will buy enough of their product to pay for the creation of the infomercial, purchasing airtime, all the infrastructure that goes with order placing, fulfillment, shipping, etc. and then to give them a profit. The Showtime Rotisserie oven, for instance, generated a billion $$ in sales during its run. Keep in mind as well that we're just now at the tail end of summer. Once October kicks in, you may see more infomercials running to try and drive Christmas/holiday sales.
Earlier on, there were infomercials for things like steam irons, polymer car waxes, sandwich makers, cookware and the like. It seems they'd find or invent a marketable product, create an infomercial, overhype and promote it, generate millions in sales relatively quickly and then once interest started to cool off, they'd move to the next product.. The items they weren't pitching as actively on TV anymore would usually find their way to the "As Seen on TV" sections of some stores, or being hawked to passersby in mall kiosks. There were a fair amount of infomercials about flipping houses or making money on real estate back when, but so many of those hosts such as Don Lupree got into hot water and in some cases lawsuits due to misleading claims they'd made or shady business dealings. At least the car wax ones and the infomercials from people like Mike Levey could be somewhat entertaining. The ones that got monotonous were the ones for cosmetics (sometimes parodied brutally by shows like SNL, MadTV and In Living Color), vitamin, supplement and snake oil sales, and gimmicky crap like speed reading courses and the like. Amazing sometimes the crap people will fall for and buy.
Most TV ads now seem to be overly repetitive standard-length commercials that run during regular spot breaks (the guy who cuts open a boat and fixes it with Flex Seal before speeding across a lake in it, for instance). Obviously since most music is downloaded these days, most all the Time Life Music infomercials and even spots for record and CD sales are long gone.