Profit.
I purchased Bitcoin because of the possibility of market price increase over the years and that simply means profit. I stayed and became still with my holdings because of profit as well. No big profit will be earned by a single night alone. Some people are even holding their investments for a decade or more because its market price has the potential and such capability to do so given that more countries, as time passes by, are recognizing and considering adoption of this technology in general.

However, Bitcoin is more known as a form of digital asset and not merely an alternative mode of payment for daily transactions. Some people find this idea negatively but personally, as long as people benefits from something despite on what way it is,  they're still good with its existence. This industry is still young and further development could take place in the future. Simply another reason to continue being involved on blockchain technology.