Smaller gauge wires work fine for speaker cable, you just need to use a lot of them.
HT used 19, 24 awg OCC copper wires insulated with air formed polyethylene, per leg, in their Pro-11 plus cable. In their new line of cables, including the new version of Pro-11, they have taken to using multiple, individually insulated wires in a range of sizes from 20 to 24 awg. Not all that different from cables that could be made using multiple doorbell wires.
HT used 19, 24 awg OCC copper wires insulated with air formed polyethylene, per leg, in their Pro-11 plus cable. In their new line of cables, including the new version of Pro-11, they have taken to using multiple, individually insulated wires in a range of sizes from 20 to 24 awg. Not all that different from cables that could be made using multiple doorbell wires.