That right there is the big million dollar question, isn't it?
My personal opinion is that since the end of World War II, nuclear, biological, and chemical weapons have always been seen as last resort, "doomsday" weapons, the application of the principle of "Mutually Assured Destruction" and all that stuff. Although these weapons have always rightly concerned us, I don't think that prior to the 9/11 period that our government ever honestly believed that our enemies would actually escalate a war against us to the level of using such weapons.
Now of course, we know otherwise, and I think it scares the hell out of the people in high places in America to know that our enemies not only hold the "keys to the kingdom", but that they would actually take it to the level that they have. Better not to have the average American people dwelling on such things like whether their next letter or bottle of medication is going to have an anthrax cloud in it.
It very rarely gets widely reported in the media, but law enforcement drills simulating an anthrax attack are done on a pretty regular basis now in big cities all across the country. It's not too hard to figure out why.
During the Cold War it was considered a definite possibility that germ or chemical agents might be used as a prelude to the Warsaw Pact invading NATO countries.
Better not to have the average American people dwelling on such things like whether their next letter or bottle of medication is going to have an anthrax cloud in it.
I went through more than one military service school regarding the effects and use of "CBR", Chemical, Biological, Radiological, (the acronym dates me to the 60's and 70's). That said, given my preference, I'd rather be "nuked" than "bugged", i.e. anthrax, or "sprayed" i.e. chemical (nerve gas). Nukes can obviously be seen when they explode and their radioactive debris can be easily detected and collected or decontaminated. Anthrax, OTOH, is extremely insidious. It can arrive silently in the mail or by corn-on-the-cob and would spread, unannounced, exponentially before it could be stopped. If Hussein, and those in his regime, were as prone to evil as we believe, then anthrax would be his weapon of choice.
As for the anthrax cases that occurred immediately to 9/11, I have no doubt that the hi-jackers mailed their letters before they boarded their aircraft prior to 9/11 and these spores spoke Farsii with a Russian accent.