I think they just say the rainy season is over after 48 hours with no rain in 50% of the country or something meteorologically sound.
I like the rain too because I don't need to water my garden, but constant rain all day for weeks gets a little tiring. It brings a lot of mould slime and bugs too. There is also the humidity. In tropical countries, I found the rainy season to usually mean an hour or so of intense rain at night.
Also, I just got a new bike a couple of days ago and I want this to be over so I can cycle without risking being caught in a downpour.
Happy cycling! I'm a cyclist too :)