Like what others have said, most streaming services will shut off automatically after a set number of hours. Streaming services pay a fee for every title they play, albeit it's a tiny fee for any one particular user. And the bandwidth they use are also expenses that they have to pay. Multiply that by millions of users and it could become very expensive for them to provide you with free streaming music.
One way around this is you can set up a routine to play whatever station or playlist that you want. Create routines to starting playing at 8am, then again at 2pm, and again at 10 pm. Or even more often if you find that your music has stopped sooner than you'd expected.