I disagree. 4G is severly limited in capacity so speed will vary everywhere, and same will apply to 5G too. Fiber has incredible capacity and can be upgraded by changing OLT and ONT equipment on both sides. It can also run multiple protocols.

2 Gbps XGPON2 is starting to roll out in my country and it's a rather simple upgrade (but costly). If your ISP isn't offering gigabit on fiber, it's purely motivated by greed and lack of competition.

Also I'm not aware of any "community fiber cabinets" limited to 1 Gbps. Are you talking about GPON or Ethernet networks? Ethernet is not FTTH but FTTN, like DOCSIS or VDSL can be.