Or, alternatively, your local ISP did not invest enough into the infrastructure and created a network that can only serve 10-20% of the population with the prom

Or, alternatively, your local ISP did not invest enough into the infrastructure and created a network that can only serve 10-20% of the population with the promised high speeds (25Mbps). Therefore, when everybody comes from work and try to use the internet at the same time, there is not enough bandwidth for everyone so it just becomes unusable.