Well because you are only allowed shampoo-
A little more than a month ago, following a long ban, Israel permitted the import of detergents and soaps into Gaza. Even shampoo was allowed. But one merchant discovered that the bottles of shampoo he had ordered were sent back because they included conditioner, which was not on the list.
Amira Hass (who was arrested by Israeli authorities when she returned to Israel from Gaza to report) continues-
The few items merchants are allowed to trade in are divided into three categories: food, medicine and detergent. Everything else is forbidden – including building materials (which are necessary to rehabilitate Gaza’s ruins and rebuild its infrastructure), electric appliances such as refrigerators and washing machines, spare machine and car parts, fabrics, threads, needles, light bulbs, candles, matches, books, musical instruments, crayons, clothing, shoes, mattresses, sheets, blankets, cutlery, crockery, cups, glasses and animals. Many of the banned products are imported through the tunnels and can be found in Gaza’s markets.
Pasta, which had been forbidden in the past, is now allowed, after U.S. Senator John Kerry expressed his astonishment at the ban during a visit to Gaza in February. But tea, coffee, sausages, semolina, milk products in large packages and most baking products are forbidden. So are industrial commodities for manufacturing food products, chocolate, sesame seeds and nuts. Israel does allow importing fruit, milk products in small packages and frozen food products as well as limited amounts of industrial fuel.
Full article here.