Off road is fun for many reasons. The two obvious ones are:

1) See what you can achieve on this particular cycle. Full suspension, fat tyres, multi gears, you need to find drops and rocks etc; fixed wheel, no suspension, skinny tyres, you can find a challenge locally.

2) Just enjoying exploring the woods and hills.

I've seen plenty of mountain bikes trundling along the main forest tracks while I've been exploring the narrow tracks and tricky bits on fixed, or on unicycle.