Copper access networks are a compromise that was reasonable in 1998. A twisted pair can carry broadband, but its usable bandwidth collapses with distance from the cabinet, and in Bangladesh the cabinet is often further away than the operator admits.
Fibre does not care about distance in the same way. A single GPON port reaches 20 kilometres with no active electronics between the exchange and the subscriber, and it is completely immune to electromagnetic interference — which matters when your cable shares a pole with a transformer and a dozen unshielded power lines.
The practical difference shows up during the monsoon. Water ingress into a copper joint raises attenuation and the line either slows down or drops. A fibre joint exposed to the same water keeps working, because light does not short across a splice.
There is a commercial argument too. Once the fibre is in the ground, upgrading a customer from 20 Mbps to 100 Mbps is a configuration change, not a civil works project. That is why we build only fibre and why we can quote an upgrade the same day you ask for it.
If you are choosing a provider and the answer to "is it fibre all the way to my wall?" is anything other than an unqualified yes, you are buying a technology that is already obsolete.