not in the shadow of somewhere larger on a main line (e.g. Gloucester is close enough to Cheltenham)
I think you'll find Gloucester's population is larger than Cheltenham's. Its just that Cheltenham's station sits on the mainline and is easy for trains to call at, where as Gloucester's is just off the mainline and forces north-south trains to reverse which typically takes 10 minutes so I'd class it as more operationally convenient for XC.
Weren't Gloucester's woes self inflicted, as the city lobbied to get the through station (Eastgate) closed in the 1970s in order to bring about road improvements?
The line linking the old Eastgate station to the main north-south mainline made it relatively easy for these trains to call at Gloucester. However the line had 4 or 5 level crossings in the city over busy roads that caused gridlock when the barriers were down to allow trains through. It would have been near on impossible to remove the level crossings without demolishing a lot of houses either side to build over/under bridges and would involve major alteration of road layouts so obviously not popular with locals. I suspect the road lobby had a good foot in the door by this time encouraging the council that removal of the line would be good for the ever increasing number of cars on the road. BR were also on a tight budget and had wanted to rationalise the stations in the area for some time. They were happy to divert most of the trains that did call at the Eastgate station to Central, so the line's fete was sealed with it ripped up, the station demolished and the land sold off. An Asda supermarket now occupies the site of the station and the inner ring road was expanded onto part of the former line.