Why Mac Internet speed is always so slow

When I am in my country house with very slow internet, like 2MB bps, Every time I switch to use Mac I have to switch back to use Bootcamp PC due to internet speed issue. In the big city, the internet I use have broader band...but still this bug has been in Mac for over a decade and I am very curious why it has never been fixed. This problem occurs not only in WiFi connection but also on Ethernet connection.