maintaining a pump track would be a nightmare
public use would turn to un-sculpted mounds of dirt quickly. (winter park's pump track turned to junk over the course of 6 months, people at the end of the season were complaining) people rolling over and off berms, casing pumps, falling, overall damage in general. also will need a water source and do it without tarps to protect from weather.... i would have to agree, nightmare.

private use wouldnt be so bad (at least I keep telling myself that). still a ton of work no matter how you justify it.