Sometimes its no fault of anybody, its just the length of the queue. E.g. green card renewals, simple, used to be done in 6 months or less. Now it is assumed that it will take 24 months. This i90 has no burden of proof or stuff, its just simple pay fee & get new card. So, sometimes applicant thinks rightfully they are stuck in there for ages, and USCIS has no saying in hiring new staff or implementing new laws or changes.