How are arriving aircraft assigned to runways? A similar question to this one was asked before, however my question is not about who assigns runways to arriving aircraft, but what the reasons behind those decisions are.

As an example, let's look at Frankfurt EDDF with four runways (map here). 18 is only used for departures. Of the three parallel runways 25L/07R, 25C/07C and 25R/07L, one is usually also used for departures, leaving two of them for arrivals (from my experience, usually 07L/25R because it's for landings only, and then 07R/25L).

Besides runway length (as discussed in the above referred question) and width, what factors into the decision of which of the two arrival runways an arriving aircraft is assigned? (and other than that it is regulated that certain types may not land on 25R/07L such as A380, B747).

Can airlines / pilots request a runway? In particular, landing on 25R in Frankfurt should be pretty unpopular due to the long taxi time to the terminals.
Arrival and departure runways are mainly assigned due to airport flow. Each airport has its own set of plans of which runways to use, how to taxi to these runways etc. If everybody is moving in the same direction, things go smoother.

Pilots and airliners can request a specific runway, but the request may be denied unless the aircraft has an emergency. Generally the reason is to shorten taxi time, and ATC may grant the request if traffic volume is low. For example, in an airport with a parallel runway configuration, a cargo plane may request the one closer to the cargo terminal.

At some airports, a runway switch may be performed fairly late during the approach. For example, the visual approach to 13L/13R at JFK is largely the same - the only difference is timing the final turn*. Occasionally you will hear pilots requesting the other runway on ATC recordings on YouTube.

For specifics such as which runway goes to which airline, they are local to the airport in question and outside the scope of this answer.

*occasionally, the pilots got it wrong and line up for the wrong runway