Even though bitcoin shot through the roof last year, there where a few things that really hurt it as a currency. Constant regulations and bans imposed on using the currency around the world, and the increasing costs and wait time of transactions.

While there's not much that can be done when a government steps in to regulate it, the transaction costs on the other hand are being handled by the market. Bitcoins coding makes it really limited in the number of transactions it can sustain at any given time, as you saw last year when it was hitting around 20k there where a lot of transactions overloading the blockchain which put excessive strain on the wait time and fees. When the smoke began clearing around 10k and there where fewer transactions the currency was able to begin stabilizing again.

However recent new innovative technologies such as lightning/hash networks have been in the works to speed up and facilitate the transaction problem. Large companies who've invested in equipment that can handle strain of the blockchain are outsourcing their processing power locally to individuals who don't have the means to download and maintain the entire blockchain.

Normally last year I would have said bitcoin has an upper limit of value (20k for instance), where once that limit has been reached it would be too expensive to transact with until the market slows down and corrects itself. But now with recent innovations the possibilities of it surpassing it's former highs are likely, to what extent I'm not sure but I'll be keeping an eye on it.