There is a severe shortage of qualified sign language interpreters. The interpreters who are qualified are in demand and can be quite expensive. Interpreters often need to be booked weeks or months in advance.
There are interpreters available through remote video interpreting services (VRI) where the interpreter and the clients are projected onto a screen from another location through a webcam. The United States has several companies that offer VRI services (known as video relay services) for phone calls through their websites.
Interpreting services cost money, however, and most places do not want to pay. They would rather use unqualified volunteers or the children of deaf family members to save bucks, not understanding the potential harm they could be doing to their deaf clients or the volunteer interpreters.
This practice is still common even though some countries such as the U.S, Canada, and the United Kingdom have laws in place that require sign language interpreting services in most settings.