The price of gas bottles

The butanero (gas man) has just been past. Driving around the small streets in a small van type thing yelling "Bonbones". Never did understand the bonbones thing, so if your spanish is better than mine please enlighten me.
Anyway, I had an orange bottle to exchange and once again got a surprise. The price this time was 12.60 euros. Everytime I need a new bottle it seems the price is a little higher and it has doubled in the last 5 years.

I wonder why that is? Maybe because there is now city gas in the larger spanish cities, and it is not so profitable to eb a gas man anymore? Or are they just following the higher oil prices?