If I'm signing my own bank check, I'll do it with the minimum expiration, one day, so if I lose I will have no problems, I can re-sign other.
But you're going to sign a check for me, I prefer that the date is long, if it is one day and I have not received, I will have problems, or have to go back to ask you to do me another.
The same with a $100 bill, if you'll give me, better not expire, do not worry, I'll take care not to lose, but if I print, better expire soon.
There is no advantage at all in a short expiry date on the certificates unless you are yourself which signatures.
I think they are excuses, not reasons... the real reason is that they do not want responsibility, or lack the resources to higher expiration.
If indeed it is an advantage for us, and want to help us... given the option of expitación of 90 days or a year.
Note: Although I appreciate it, I do not need anyone educate me on automate task, or as I do my work.