Answer:
The problem with variable rates is that they vary, i.e., they might unexpectedly increase and the increase might be pretty significant. One of the main factors leading to the Great Recession was the housing bubble and the increase in mortgage interest rates. Normally, interest rates tend to increase, they might sometimes decrease, but generally they only go up and up.
Even though the fixed interest rate might be higher, it will not change and that guarantees that you will always pay the same amount and that you can prepare your personal budget to cover it.