1. Consumer broadband speeds rarely exceed 1Gbps
2. 1Gbps Local network transfers are seldom slowed by the network (as large file work typically involves HDD still)
3. Where local network transfers are impeded by the network speed the transferring itself isn't a frequent enough and blocking thing that people feel they need to fix it... they just go make a cup of tea once or twice a day
4. There are a lot of old network devices and cables out there, some built into the fabric of buildings (wall network sockets and cable runs)
5. WiFi is very very convenient, so much so that 250Mbps is good enough for almost anything and most people would rather be wireless at that speed than wired at a much higher speed (gamers and video professionals being an exception)
And ultimately, the cost and effort of investing in it doesn't produce an overwhelming benefit to people.
Even in quite large offices, it's hard to argue that this is worth it when the vast majority of people are just using web applications and very lossy audio and video meetings across the internet.