At modern fighter is not a Honda Accord. You don’t just hop in it and drive it around for months until you finally have to take it for a one-hour oil change when the light comes on. If anything, they are far more akin to high-end sports cars that require a lot of expensive TLC to keep operating. The F-22, in particular, is more analogous to an exotic supercar or even a high-end race car than anything else. It requires dozens of hours of maintenance for every single flight hour and deep maintenance can take days or even many weeks to accomplish, depending on what is needed to be done and availability of spare parts, which can be scarce.
On top of some aircraft being sidelined for extended periods of time for repairs, others have to go through periodic planned servicing, discreet component inspections, and invasive phase inspections, the latter of which sees the aircraft largely disassembled before being arduously put back together and flight tested before returning it to the active flight line after all its issues, or ‘gripes,’ are worked out. In other words, many of these operations are not ones you can simply stop and reverse to rapidly generate the aircraft into a flying condition in a matter of a day or two—in some cases, not even close. There are always a number of aircraft going through these planned maintenance intervals, that way a squadron’s inventory can remain fairly predictable given the demands being placed upon it.