You can get sub-$500 laptops with SSDs but they're all extremely low-capacity (the HP Stream 11 is $200 and has a minuscule 32GB SSD with ~8GB already eaten with a "recovery partition") and often are netbook-esque machines with drives that cost way too much to upgrade because they're not 2.5" SATA form factor. I have made a fair amount of money buying $350 laptops, slapping a $60 120GB or 128GB SSD in place of the 750GB 5400RPM drive, doing a fresh junkless reinstall of Windows, and reselling the units for $500. When you show someone a cheap-ish laptop with an SSD booting up to a fully started desktop in 20 seconds, they literally see the value of SSD technology.
As you've pointed out, no major manufacturer seems to currently offer a low- to mid-range ($300-$500) laptop with a reasonable SSD as standard equipment. If they did, they couldn't milk the margins on SSD upgrades for their overpriced "enthusiast" laptops. Laptop makers tend to have thin margins on the cheap machines at their base model specifications and make most of their (consumer-grade) profits on sales of accessories (AC adapters, extended-life batteries) and heavy markups for each bullet-point in their "customize this computer" system upgrades.
In my experience, most people also fall into two data usage categories: people with 0GB-50GB of data (mostly iTunes libraries, Word docs, and maybe a few photos) and people with well over 100GB of data (media professionals, obsessive family photo shutterbugs, heavy gamers, people who would download a torrent of "the entire bloody internet," etc.) The majority of them fall into the first category and the ones in the second category will usually spend a lot more money on equipment because they're a different class of user and they know more about computers and how to meet their needs.