It's not a big deal, but it's wise to always consider who might use the information you put on the web and for what purpose. When you do a lot of posting on FR, it's easy to start unconsciously thinking that this is a closed network and only FReepers read your posts. Of course it is not, so I'm just suggesting that you always consider who outside of FR might read your posts. If there's no particular benefit to anyone from talking in detail about explosives or weapons, then why put that knowledge out on the web?
Once the road to knowledge is closed, the journey itself loses meaning.
Probably because hexamethylene tetramine is slightly more of a nuisance (though still easily accessible) to procure and/or fabricate compared to acetone, which you can get at half the stores in town. Also, it does not appear that they were particularly selective as it stands. If they really cared, they could have fabricated much more powerful explosives of marginal stability relatively easily. They were just looking for a cheap-n-easy high explosive, and TATP was it. Difficulty of detection might have also been a desired property, though I would have gone with a different family of cheap and stable high explosives to do the same job (which I will refrain from naming) had I been doing it. But then, I'm neither a terrorist nor an idiot.
This is very rusty knowledge off the top of my head; I haven't been involved in that line of work or chemistry for many years. It is fortunate that most terrorists are only slightly more technically competent than crack-addled monkeys.