Good question...

For several reasons.

Logistics: Flares are considered ammunition, and as such requires special handling, transport, and storage. A life raft facility can easily exceed its rated explosive storage capacity when servicing rafts from a large population ship. It's a reoccuring expense as the flares have to be periodically replaced. Non-pyro signals just use batteries. After initial acquisition, the cost is a few bucks for new batteries for subsequent servicing.

Usage: If a military vessel is sunk during combat, there is a high probability of fuel on the water. A flare burning at 3500 F degrees can ignite the fuel if it were to come in contact with it. They also pose a hazard to the raft and survivors if misused or if they malfunction.

Training: It's difficult to provide hands-on training with flares due to the expense and hazard. Non-pyro kits can be distributed to all the ships and training commands such the sailors can train with them, making them more effective and safe to use.

Regards,

Tom A.