"Simple FOIA Request?" There's no such thing.
I've worked with a few Federal agencies and watched how much time is spent on FOIA requests. It takes a lot of effort to get some of the data together and along with the approval process, i.e., "Will this compromise any ongoing operations? Does it need redaction based on PII and other rules? Where is the data?" Then there's the approval of the response which always has to be reviewed by Lawyers, discussed in triplicate and then dispatched to the requester. Some agencies have huge departments just dedicated to handling FOIA requests and even with that I've seen them impact day to day operations where front line management has to deal with data collection and validation as well.
To a point, FOIA is a great law and I think it's definitely opened up the inner workings of gov't. A lot of this would go away if the gov't was more transparent to begin with especially in matters not dealing in PII/4th amendment issues (Tax Returns for individuals) or national security. I do think some FOIA requests are fishing expeditions and in all cases the costs should be paid for by the requester. It's also not applied uniformly across all agencies and while the National Park Service may respond quickly, the DoD or DOJ may take years or in the case of the IRS or State Department might get derailed altogether.