Hello Rocky
The reason why Frame Relay is declining in use is primarily because of the competition it’s facing from cheaper and faster technologies such as Cable, DSL, Metro Ethernet and MPLS, all of which, with the appropriate configuration, can outperform Frame Relay in most cases. Also, these technologies are more compatible with the LAN technologies used while Frame-Relay is completely different and requires the appropriate termination equipment (CSU/DSU etc) at the customer premises.
Limited bandwidth is not so much an issue as cost per bandwidth unit is. Getting a fast Frame Relay connection that is comparable to the aforementioned technologies can become prohibitively expensive. The non-broadcast nature is an issue, but can be dealt with relatively easily.
I hope this has been helpful!
Laz