I reckon most give up at guitar because all they do is learn covers/play on their own. Covers are always a good starting point, cos its not that hard to sound quite nice with a simple chord based strummed song. I started that way too, BUT...I do believe most pack it in because they then just stick to that method. Honestly believe the trick is to just not mind sounding shite and just enjoy making your own personal noise too, or even just jam with some friends. Convinced so many don't get better because they're just trying learn songs they love, and it often becomes a chore, and a frustrating one at that when you're not quite as good at that song as you want to be. It's easy to lose interest then, because they're not getting anything back at it. They're also not exploring the fun creative side of guitars, which is what most of us actually crave.
All of the above is why I think its important that when you've got a bit of confidence, just play about and actually just enjoy making noise with a guitar. Or find someone to just have a jam with and make a load of noise. It isn't like learning a song that has a strict way of playing, which means technically you can't really be getting anything wrong, and it kinda feels nice to not be limited by anything, and you can't really sound shite either, cos its just your own personal ideas. I mean they may sound a bit shite, but they're not 'wrong' are they? Cos its entirely subjective. Plus there is nothing better than making a load of noise with a mate. It's ten times more gratifying than nailing a perfect cover IMO :)
Maybe that's just me anyway. Can only speak from my experience there! I'm bang average at guitar, but I was basically the lead guitarist in a few moderately successful bands for years. I just had an ear for a melody. Terrible at covers, mind. If you put me in a room, there's usually no way I could impress someone with a guitar on my own, but if you put me in a band jamming I could write a nice melody that people would usually enjoy listening to. My mind just isn't wired the covers kinda way, and chances are the minds of most aren't, but they just go down the cover route and eventually get bored. I'd rather write something with a friend instead of learn something. If i'd have stuck to just doing covers i'd have got bored very quickly. I reckon most don't realise this.
Long story short - defo learn some covers, but also defo try writing some things and just enjoy making a fuck load of noise! That's the point of guitars really.