Dear friend!
The access of using DSL network or PON network mainly depends on the decision of local telecom operators. Because the DSL network is earlier than the PON network. In this case, DSL has achieved a large area of coverage. If the PON network composed of optical fiber replaces the DSL network completely. The cost may be high. So some parts of many countries are still preserved.
In addition, VIP users of carriers usually access the Internet through PON networks because the PON networks provide higher bandwidth (up to 10 Gbit/s at present).
Thanks!