The appeal here is simple value. For $5 for 50 cards, you're paying 10 cents per card which is effectively floor price on Pokemon cards no matter what format. The individual booster packs cost $4 to $5 and contain only 10 to 11 cards, so you'd be paying $20 to $25 to get the same quantity through the traditional retailing method.
It just seems like it would be too much hassle, and that's not to mention everything that happens around the game. When I do hear stories about the TCG, they're usually stories of controversy . Images of people nearly destroying the Van Gogh Museum in order to get exclusive cards and merchandise to sell online, as well as grown-ass men fighting and camping out for cards outside of GameStops, are seared into my brain.
For those that don't know, the "Prerelease Raichu" card is the stuff of legend. According to reports dating back to the late '90s, around 11 copies of the original Raichu card with "PRERELEASE" text stamped in the corner of the artwork were accidentally produced by Wizards of the Coast employees. These cards were mixed in with pre-release Clefable cards that were given out at events in the '90s, and they were supposed to have been destroyed, though a few were supposedly saved by WOTC workers.