Free trials are wonderful. You get to test a product for a limited time and see if it's worth the investment. Back in the day, you only ever really needed an email address to sign up for a free trial.
This has changed, and nowadays you'll always be asked for a payment method. Most sites will also try to justify this hurdle with plain excuses, like for example:
We ask for a payment method to ensure you don't have any interruption in service after the free trial.
That's just another way to say, if you forget about us, you'll be forced to pay us. And it's also a great counter measure against people who would otherwise constantly make new accounts for the free trial.