Ive seen lot of answers like, market will not have morethan 21M BTC and that amount will be saturated by 2140, hence there will not be any inflation etc. But what I do not understand is, if a currency is not using (in trading purpose you buy something with that money), what is the logic behind the reason of value of the money goes up ?
Firstly, Bitcoin is a valuable asset and that the more it gets mined, the lesser it becomes on a daily basis as you know that there are just 21M coins to be there in total. Take it like you are not living an extra day in your life, but you are losing one.
Now, don't compare it to a currency because a currency is something termed as "stable" and Bitcoin is volatile. The interest of investors, their recommendations to general public and mainstream media are the three most important reasons why Bitcoin is gaining too much value. You must also be aware of the fact that everyone was interested in a lot of free money (generated through hard forks of BCH and BTG) and that, they say that the value of Bitcoin will only drop once these BCH and BTG will be fully released to their owners but I think that whatever will happen, Bitcoin is still very cheap and it won't be expensive for me unless it goes over a $100k.