Well, by regulation, an aircraft is a “national property”, so a blast in an aircraft is seen as “national incompetence”. The security check is just a filter, an attack there is seen as general terror. The stakes are very different. It is also easier to de-escalate someone with a gun or other dangerous objects at the security check, people at that location are well trained to handle such situation and extra support is just a radio away, in aircraft, not only is the situation extra dangerous because other people sitting will act immensely irrationally or panic, the crew is only trained in minor de-escalation, and it is difficult to call a backup security in mid air and any shots fired in that environment is 1000x more dangerous.