Practical information not only for parents
The reasons are sure to find many. I will try to list the most important ones:
The unique sound characteristics, eg. Tone color.
Versatile usage. Guitar can be used in almost all musical genres (classical music, folk, rock, jazz, blues, flamenco, hardcore, metal, ...).
The relatively rapid achievement of playing results. This is of course very individual, depending mainly on hard work and talent of the pupil. I am referring to minor results that encourage us and cheer. For example, mastering simple songs accompanied by two chords.
The possibility of singing while playing. Not every instrument allows us singing during play.
Easy portability. The guitar is relatively lightweight, it can be transmitted in holster on your back.
Relative price affordability. In comparison with other instruments is one of the cheaper ones. At least in terms of price and quality.