I disagree. The reason people abandon guitar at such rates is that it is far more complex than, say, the piano. I don't have data to back this up other than the fact that I play both instruments, my wife plays the piano and we have taught all three of our kids.

At some stage on the guitar your left hand (assuming right-handed player) has to start doing some really unnatural and difficult things for you to be able to play anything interesting. Then there's the fact that notes are found in multiple places on the fret board and certain sets of notes cannot be played effectively unless you switch your left hand to those other "magical" positions.

Then there's the need for precise placement of the left hand fingers as they land on the string/fret in order to avoid making weird noises.

If you are learning classical guitar, there's keeping your fingernails to the right length and shape and constantly having to fiddle with them. If you don't have good nail genetics (my case) you have to resort to nail strengthening magic cures and even such extreme solutions as painting on a couple of layers or epoxy onto your nails to thicken them up and allow you to play without them breaking.

For example, my right hand's thumb fingernail is weak and quickly develops this little notch where it contacts the string. I have been suffering with this since I was a kid. It's a pain in the ass. I've done some crazy things at times to deal with it, like bonding a thin piece of carbon fiber sting to the very edge of my nail.

Being creative and improvisational with the guitar is hard and takes a lot of work and study. You need to get past all of the above and that means at least a year, if not two, of daily (and correct) practice.

Piano is easier. You remove a lot of the instrument and musician "organic" factors the guitar introduces. With proper hand position and fingering progression can be steady. It is a one-to-one relationship between note and key, which makes it magical when compared to the guitar. Chords and arpeggios written for piano are generally within the domain on a single hand. Even if it takes two, it's no big deal.

I truly think that someone can achieve much more satisfying results by practicing piano one-half to one-quarter of the time of someone achieving equivalent results with guitar. And, ultimately, I think this is the reason so many people quit guitar early, it can be very frustrating when compared to the piano.