The airline responded on Twitter saying, "Jetstar limits the carry-on baggage to 7kg for the safety of our customers and crew. Kindly visit http://bit.ly/2qx69Z8."
In 2014, Jetstar reduced their carry-on allowance from 10kg to 7kg “to ensure everyone has their fair share of locker space to store their bags," a spokesperson said at the time.
The reduced baggage is also what helps keep their fares so low.
Plus, they aren’t the only airline with a 7kg limit.
“Tigerair Australia customers are provided with a 7kg carry-on luggage allowance free of charge,” a spokesman told news.com.au.
“The 7kg carry-on allowance may be spread across up to two separate pieces of cabin baggage, including handbags and purses.”