Hercules cards were very popular with business users. They were cheap and even Harvard Graphics wasn't enough to make color worthwhile (it did stippling and lines very well).
PGA was too expensive for what you got for most users. On one technical visualization project I worked on we only got approval to move forward when we re-specced it with EGA, when it became available.
Even after VGA came out, Hercules was still common even in new systems, and most people didn't see the cost of a new monitor worth the upgrade. Most folks who stared at a monitor all day for a living resisted the change as they weren't comfortable looking at the awful 60Hz images most "business priced" low end monitors put out. They were usually vehement that only an amber or green screen would let them work without headaches.
In my own home, my wife refused to shift off her Hercules card (one of the later enhanced models) until I paired up a high quality XGA-capable Orchid card with a high refresh rate Trinitron monitor for her. She couldn't complain about the price since they were developer loans the client didn't want to pay to ship back after the job. Still, it lived alongside the Herc card in her 386 (the latest processor, that she was up for--with math coprocessor, Weitek if possible) for eight months until she started to decide color wasn't so bad, and might even turn out to be useful.
