Island drains deal with sand and with guests, and in a villa they also deal with whatever the neighbours send down.
Sand settles rather than washing through
Every shower in a beach property takes in sand over a season. It is heavy, so it collects in traps and low spots and gradually narrows the line. Jetting flushes it out; a cable simply makes a channel through it.
Shared stacks in multi-unit buildings
If you are in a villa and your drain is slow, the cause may not be in your unit at all. A stack collects from everyone connected to it, and grease from one kitchen affects the units below. Where a building has a history of this, scheduled jetting of the stack costs far less than repeated individual call-outs.
Rental turnover
Guests do not know your plumbing. Wipes, cooking grease and sandy towels rinsed in a shower all end up in the line. Clearing drains between bookings is far better than a blockage in the middle of someone’s stay.
Outdoor showers
These take the most sand of anything on the property and are almost always forgotten until they stop draining.