Remember time when you had to download the whole website in order to search through the needed information? You had to dig through the whole mass of data in order to get what you really need. That was bearable when you work on PC, but became totally inappropriate the time you appeared to be working on any mobile device.
The reason is that the connection is unfortunately not as fast as on local PC. Moreover you have the limited screen and cannot accept there all the information at once.That is when the single page web applications appeared to be far more popular than full size websites.
Specialties of single-page web apps
Web app developers composed the front end to any content database. While website programming offers you to deal with all data at once, single-page applications let you pull the needed piece of data right into your hands without losing any time.