This is used as a dark pattern. Entering a credit card to try out a service without being able to see how you would cancel is asking a lot of faith in a service you are trying out. Asking for a credit card on signup means I've already decided you are worth it. I hope you spent a lot on marketing to prepare me.

Free trials can be limited in terms of services. Many times free trials are not necessary. If someone is willing to enter a credit they will pay a small amount.