It's more likely because you can't achieve modern security levels with cryptosystems built on the DLP or IFP at acceptable performance. Suite B aims for 128-bi

It's more likely because you can't achieve modern security levels with cryptosystems built on the DLP or IFP at acceptable performance. Suite B aims for 128-bit or 192-bit security levels; for comparison 1024-bit modulus RSA is currently thought to provide 73-bit security. (The next natural question is why the internet community is still failing to widely deploy cryptosystems with appropriate security levels. I don't know. But HTTPS, OTR and DNSSEC are all built of cheese in this respect.)