Simply because "bomb" dogs, like "drug" dogs are a scam to give the police a legal excuse to violate your rights. The dogs don't detect bombs/drugs, they detect cues from the controlling officer.

https://en.wikipedia.org/wiki/Detection_dog#Criticism

  The law was reviewed in 2006 by the New South Wales Ombudsman, who handed down a critical report regarding the use of dogs for drug detection. The report stated that prohibited drugs were found in only 26% of searches following an indication by a drug sniffer dog. Of these, 84% were for small amounts of cannabis deemed for personal use.[27]: 29  Subsequent figures obtained from NSW Police in 2023 revealed that between 1 January 2013 and 30 June 2023, officers had conducted 94,535 personal searches (refers to both strip searches and less invasive frisk or "general" searches) resulting from drug detection dog indications, with only 25% resulting in illicit drugs being found.[28]

Bomb sniffing dogs can't detect every explosive compound under the sun. They're trained on some of the most common ones but there are almost infinite variations of explosive chemistries.

"According to Sky News Arabia; Mossad was able to Inject a Compound of Pentaerythritol Tetranitrate (PETN) into the Batteries of the New Encrypted Pagers that Hezbollah began using around February, before they even arrived in the Hands of Hezbollah Members, allowing them to Remotely Overheat and Detonate the Lithium Battery within the Device."

the idea TSA security has always been a farce, detecting only the crudest methods of attack.