I live on an island. Most of my customers are abroad.
It's a large island, and I'm at the northern end. the biggest city, where I also have some customers, is at the southern end and is too far to drive for a short visit.
It's a cool temperate island, so sunny holidays also require flying.
To cap it off, all my siblings, aunts, uncles, cousins, nephews & nieces and one of my children live on the far side of the world from here.
And you ask why I fly?
99% of the time I deal with my customers and colleagues by phone, email, Skype, and video call.
But those dealings are most successful with the ones I've actually met face to face at some point.