Probably what did for Bath was the cuts in BANES council funding and maybe they also lost the use of the Pavilion at affordable rates. I also think that another major reason was that the very nice lady, Eloise, a key force behind the scenes in managing the Jazz content of the fest, sadly passed away. It was never really the same again after her passing. At the end of the day and above all else it is people and their dedication that makes these things happen (which is why Swanage goes from strength to strength).
It was at its best I guess when I lived in the city several decades ago (it was actually possible to afford/buy a house there then). On quite a small scale when it start out and concerts very reasonably priced for a fiver or so, even at the Guildhall etc. You could even buy wine from the glass at the gig - classy !
I feel somewhat the same way I'm afraid !