.... So why doesn't electrum use more words or this program to generate the private seed?
Because the "seed" is not actually words... The seed, like other HD wallets, is actually just a (VERY) large number. The seed mnemonic (ie. the words) is just a method for representing that very large number that makes more sense to humans and is (somewhat) less error prone to transcription errors that attempting to write down a 128 char hex sequence. 
In any case... you CAN use custom word lists to build a seed mnemonic if you wish... this is even mentioned in BIP39:
The conversion of the mnemonic sentence to a binary seed is completely independent from generating the sentence. This results in rather simple code; there are no constraints on sentence structure and clients are free to implement their own wordlists or even whole sentence generators, allowing for flexibility in wordlists for typo detection or other purposes.
The problem is that by using custom systems, you remove compatibility with other wallets... so you'd be effectively locked into whatever wallet you were using.Also, as previously mentioned, it isn't the length or complexity of the words themselves that protect you... it is the entropy used to initially create the sequence of "random" words... and 2048 words is enough to encode up to 256 bits of entropy:
The mnemonic must encode entropy in a multiple of 32 bits. With more entropy security is improved but the sentence length increases. We refer to the initial entropy length as ENT. The allowed size of ENT is 128-256 bits.
