Why so much ground time at Frankfurt Airport? Disclaimer: Total layman here.



I frequently fly into and out of Frankfurt Airport (FRA) with regional jets (flight time advertised as 45 minutes) and one thing that everyone is always annoyed about is that you spend approximately the same amount of time in transit on the ground in Frankfurt as you spend in the air.

I understand FRA is a huge airport, but what does not make any sense to me is that you...


...have to walk 10 min to the gate
...must spend 10 min on a bus to get you to the aircraft
...then spend at least 10-15 min on the aircraft as it taxis to its start position on the runway


Given that these regional connection flights are always on a tight schedule, I do not quite get why they do it this way.

Specifically, can anyone explain why — in FRA — these small jets are parked so far away from their landing/starting positions when you have to get there by bus anyway?
Why bus
The typical reason you use a bus to your low-cost carrier (LCC) or regional jet is the cheaper 'remote stands'. But this doesn't mean the stand is necessarily closer to the runway where the planes take off and land.
See: Who decides whether an airline docks at a jetbridge or parks at a remote stand?
Can't be too close
A big area around the runway needs to be clear of tall tail fins, light poles, equipment, etc., as it may affect the navigation equipment near the runway or pose a hazard to landing/departing aircraft.
Example: Why do some airports park the aircraft backwards at the gate?
Queue
An LCC plane won't get ahead in line just because it's parked closer to the runway. If a plane at the terminal pushed back and started its engines before the one at a remote stand, it will typically be ahead by the time the LCC one is ready to go.
Shorter flights also typically use a more congested airspace (they don't fly too high, the flight is short, and it's busy near airports), so there might be a delay in releasing that flight.
Remote stand analogy
I'm not sure which remote stand you typically use, but also in airport design it's fairly common to have the remote stand share the same taxiway (the road planes use to get to the runway) as the terminal.

(Google Earth - FRA)
Think of it like this, there's a road with a mall and its fancy parking on one side (1), and the cheap parking across the road (2). Regardless of where you park, when it's time to reach the highway, cars from the two parking lots will eventually merge (3).

That being said, 15 minutes to taxi to the takeoff position on the runway (not including the time to start the engines and to get the taxi clearance) is actually really good for a major airport such as FRA. Jetliners typically take 90-degree turns at slower than 15 km/h, and 40 km/h is common for straight lines. With a taxi distance of 2.25 km (example shown above), we are looking at a delay of ~12 minutes. FRA handles ~74 movements per hour (takeoffs and landings), assuming they use 3 runways, it's a takeoff every 2.4 minutes on your runway, or like waiting behind 5 other planes.