If those words were used as an alphabet then they would define a 2048^12 or 132 bit key space.
The word lists are instead hashed (see BIP39) which gives an approximate entropy of 2.62*4.5*12 = 141 bits.
FYI BIP-39 (and Electrum 2.x) starts with a specific amount of entropy, and then
derives the words from that entropy, not the other way around as you implied. Typically, this is 128, 192, or 256 bits for 12, 18, or 24-word long mnemonics.
(and of course the hashing which follows does nothing to increase that initial entropy)