It is true that bitcoin have increased geometrically over the years,. And one of the reason for the success of bitcoin is halving that occurs every four years making it possible for deflationary effect on bitcoin to take place.  Another point is the adoption. FYI,  bitcoin is not  all stable either, we have seen bitcoin flunctuate s lot over  the year.  Some altcoin will definitely at some point hold their own and become popular like bitcoin.  Ethereum is an example of this!