Not all of our roasters heat seal their bags. Good news, it doesn't affect the taste, flavor or freshness of the coffee in any way!
The 1 and only reason has to do with the de-gassing of freshly roasted coffee. After coffee is roasted, the freshly roasted beans slowly "de-gas" and give off small amounts of CO2 for a 3-5 day period.
If the bag is left sealed, it will actually give off enough gas to fill the bag like a balloon and often times pop. Therefore, coffee roasters will have either a 2-way degassing valve on their bags and/or they will leave the bags unsealed altogether.