The processing times at USCIS do not make sense. Many times in government offices this is attributed to backlog and understaffing. However if this was the reason the backlog would constantly grow and processing times would constantly increase. If the processing time stays the same it means that either it really takes 2 years to process a green card application and 5 months to process advance parole applications etc. or the office is making sure that there is always more work than can be handled and they look busy and need more resources. making sure nobody gets fired.
Today to process advance parole or request for travel documents takes 6 months if approved it is approved for 1 year so you have to apply again 6 months before expiration.
I think that first of all the reasoning for a request for travel documents should be checked. Once someone applies for a green card when he is in the USA at that moment if he leaves the USA his application can be terminated. Basically he becomes a prisoner and can not leave the country without getting approved travel documents (advance parole) which takes 6 months. Someone that has a business and needs to travel or has family issues that need to be tended to in his origin country is affected by this rule the minute he applies for a green card.