I was thinking it was due to the lack of several coats... but that was about what I was seeing too... 3-4 months. Yeah, it's easy to re-finish, but I'd rather sail.
As it is, I sort of do it on a 6 month schedule... light sanding to get rid of the crazing, then try to get down a couple of coats... but when the humidity is high... ie late night and early morning low clouds and fog (standard broadcast weather report for certain times of the year...) you can't varnish.
I tried to beat the weather a year ago last December and just wrapped up my varnishing for the day about 2:30 in the afternoon... perhaps 60-70 percent of my brightwork... when a massive thick fog rolled in... so thick I couldn't see the docks a 1/4 mile away. I had a bad feeling when I left. The fog lifted just around dusk, and then came back just as thick in the early morning. When I went down to the boat later that next day... all that I had applied Le Tonq to, had gone white... and it was soft and sticky. I waited until summer and then worked to remove it. Ug what a chore. (later someone told me about a varnish remover from Home Depot... )