Most people saying this are looking at bitcoin continuing its past long term hyperbolic growth rate, if they’re working off data. As shown in this log graph I recently constructed of bitcoins price from 2010 to early 2018 - https://imgur.com/gallery/9iF3t - there’s a fairly linear upward growth in bitcoins value, and if this same long term hyperbolic growth rate the last 7 years is projected 7 years into the future then bitcoin will have a value of $1 million in early 2025! It must be emphasised however that this is purely a ‘projection’, and is not a ‘prediction’ of what will happen.

But I do believe there are good reasons to think that the hyperbolic growth of bitcoins price the last 7 years will continue in the next few years, and that bitcoin will hit a value of $1 million in the mid to late 2020’s! I feel the later generation blockchains and protocols being developed will allow the development of dApps that will slowly replace the current massive centralised companies and businesses we all use over the next 10-15 years, in a third technology revolution of the world. And I believe that bitcoin will continue to be one of the most important cryptocurrencies in this new world for payments as well as being an increasingly important store of value, given its robustness in use so far and the improvements to it being made by its 200 dedicated developers and its recognition as a ‘brand’ by >50% of people in the world. So I feel that given bitcoin’s limited and fixed supply its value will continue to increase exponentially as it has the last 8 years as its ownership and use by people increases from the current <1% of people who own or use it, to 10% and over ownership and use over the next 5-10 years continuing that past parabolic growth and that early adopters already owning or buying bitcoin now will make a fortune in the next 5-10 years. But there’s no guarantees in investment or life and the whole thing may become worthless, which is why people investing in crypto are told never invest more than you can afford to lose!

And in terms of your querying why the price of bitcoin has been fairly static the last 6 months at $7.5-10K, you can see the shorter term bitcoin growth rates on my log-graph as the red and green dots. There have been 5 consecutive periods since 2010 where bitcoin has a 12-24 period of upgrowth (red dots), before a 12-18 period of sideways steady price (green dots). We are currently in the sixth sideways period since Jan this year, and history suggests bitcoin will move sideways at its current price until towards the end of the year, before an upward period of growth in 2019 takes it to $50K on its long term parabolic growth line. But again remember this is a projection from the past into the future, rather than a firm prediction. But would be great to buy BTC at 7.5K and make 7x growth in 12-18 months ...