It's probably easiest to explain how this works with conventional narrowband digital modulation schemes. For a typical modulation scheme, the bandwidth of the modulated signal is proportional to the bitrate. There's also some minimum signal-to-noise ratio below which the receiver can't decode it. By sending more slowly, you get a narrower signal, which means that the receiver can listen to a narrower slice of spectrum. Even though the received signal's no more powerful than before, because the receiver is no longer hearing all the noise outside of that narrower band the SNR improves and it can decode much weaker signals.
LORA appears to use direct-sequence spread spectrum, which basically means that the transmitter applies a spreading code to convert the narrow signal to a very wide one and the receiver uses the same code to despread it again and pick out the signal. Its range improvement is still based on the exact same principle of speaking very slowly to improve your SNR though.
BLE; you're talking about power requirements of ~10mA transmit (current consumption), and averages in the <10μA range. That's the whole point of the tech. It's stuff that can run for years on a watch battery.
Now: how LORA is accomplishing such crazy long ranges when supposedly consuming similar amounts of current goes a little beyond my understanding of RF. There are a few people commenting in this thread that seem to have the knowledge, though!