The connection capacity that a BT Openreach cable can deliver might be insufficient or if delivered via an old copper or aluminium line, it might be unreliable. You may have been told that to upgrade the cable it will involve significant investment and lead time to implement. One of the most popular reasons for using a point to point wireless is that you have more control and visibility of the connection, when a fault occurs fix times are often much faster. You may want a backup to the existing connection which doesn’t use the same technology as your primary.