Why would there be a NOTAM for an airport rotating beacon being on continuously? This NOTAM currently exists at Riverside airport:

!RVS 01/014 RVS AD AP ABN ON CONS 2001141700-2001291700


The rotating beacon is on continuously per this NOTAM.  It has nothing to do with the weather.

Why would an airport do this other than in IFR conditions during the daytime?
The general convention is that the rotating beacon is only on at night or during IMC. The airport or ATC can choose differently. It would not be the norm and probably should be pointed out to pilots approaching the airport. It would also help identify the airport if there is confusion with multiple nearby airports of similar size and structure.