So the opening is big enough but Aikidoka are just not psychologically prepared, on the whole, to exploit it.
I somehow agree and disagree. Aikidoka are not only not psychologically prepared, but also from technical point of view they often don't any idea what happens AFTER they enter\irimi into attack. Such scenario with uke alive (means i.e. bouncing and disengaging only to re-attack) is never done.
On the other hand, a simple irimi is often not sophisticated enough as a solution. Advanced attacker will early see the intent of entry and will modify his behavior. Here I agree with Dazzler that we have to carefully study peoples behavior in different situations do develop our eyes. I strongly believe that aikidoka must become a master of reading body language as a first step to his mind training.